- F. Cinti, P. Jain, M. Boninsegni, A. Micheli, P. Zoller, G. Pupillo, A superfluid-droplet crystal and a free-space supersolid in a dipole-blockaded gas, (2010-08-24), (ID: 717214) Toggle Abstract
A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential \"softened\" at short distances. Using exact numerical techniques, we study the low temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighbouring droplets.
Alternative URL (local restricted copy) - A. Micheli, Z. Idziaszek, G. Pupillo, M. Baranov, P. Zoller, P. S. Julienne, Universal rates for reactive ultracold polar molecules in reduced dimensions, Phys. Rev. Lett. 105, 073202, (2010-08-13), URL doi:10.1103/PhysRevLett.105.073202 (ID: 717207) Toggle Abstract
Analytic expressions describe universal elastic and reactive rates of quasi-two-dimensional and quasi-one-dimensional collisions of highly reactive ultracold molecules interacting by a van der Waals potential. Exact and approximate calculations for the example species of KRb show that stability and evaporative cooling can be realized for spin-polarized fermions at moderate dipole and trapping strength, whereas bosons or unlike fermions require significantly higher dipole or trapping strengths.
Alternative URL (local restricted copy) - M. Dalmonte, G. Pupillo, P. Zoller, 1D Quantum Liquids with Power-Law Interactions: a Luttinger Staircase with Polar Molecules, Phs. Rev. Lett. (2010-04-28), (ID: 717205) Toggle Abstract
We study one dimensional fermionic and bosonic gases with repulsive power-law interactions $1/|x|^{\\beta}$, with $\\beta>1$, in the framework of Tomonaga-Luttinger liquid (LL) theory. We obtain an accurate analytical expression linking the LL parameter to the microscopic Hamiltonian, for arbitrary $\\beta$ and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the LL unstable towards the formation of a cascade of lattice solids with fractional filling, thus forming a \"Luttinger staircase\". Several of these quantum phases and phase transitions are realized with groundstate polar molecules and weakly-bound magnetic Feshbach molecules.
Alternative URL (local restricted copy) - K. Hammerer, K. Stannigel, C. Genes, P. Zoller, P. Treutlein, S. Camerer, D. Hunger, T. W. Hänsch, Optical Lattices with Micromechanical Mirrors, Phys. Rev. A 82, (2010-08-25), URL doi:10.1103/PhysRevA.82.021803 (ID: 717187) Toggle Abstract
We investigate a setup where a cloud of atoms is trapped in an optical lattice potential of a standing-wave laser field which is created by retroreflection on a micromembrane. The membrane vibrations itself realize a quantum mechanical degree of freedom. We show that the center-of-mass mode of atoms can be coupled to the vibrational mode of the membrane in free space. Via laser cooling of atoms a significant sympathetic cooling effect on the membrane vibrations can be achieved. Switching off laser cooling brings the system close to a regime of strong coherent coupling. This setup provides a controllable segregation between the cooling and coherent dynamics regimes, and allows one to keep the membrane in a cryogenic environment and atoms at a distance in a vacuum chamber.
Alternative URL (local restricted copy) - B. Zhao, K. Hammerer, M. Müller, P. Zoller, Efficient quantum repeater based on deterministic Rydberg gates, Phys. Rev. A 81, 052329, (2010-05-21), URL doi:10.1103/PhysRevA.81.052329 (ID: 717186) Toggle Abstract
We propose an efficient quantum repeater architecture with mesoscopic atomic ensembles, where the Rydberg blockade is employed for deterministic local entanglement generation, entanglement swapping, and entanglement purification. Compared to a conventional atomic-ensemble-based quantum repeater, the entanglement distribution rate is improved by up to two orders of magnitude with the help of the deterministic Rydberg gate. This quantum repeater scheme is robust and fast, and thus opens up a way for practical long-distance quantum communication.
Alternative URL (local restricted copy) - A. V. Gorshkov, M. Hermele, V. Gurarie, C. Xu, P. S. Julienne, J. Ye, P. Zoller, E. Demler, M. Lukin, A. M. Rey, Two-orbital SU(N) magnetism with ultracold alkaline-earth atoms, Nature Physics 6, 289, (2010-02-28), URL doi:10.1038/nphys1535 (ID: 681277) Toggle Abstract
Fermionic alkaline-earth atoms have unique properties that make them attractive candidates for the realization of atomic clocks and degenerate quantum gases. At the same time, they are attracting considerable theoretical attention in the context of quantum information processing. Here we demonstrate that when such atoms are loaded in optical lattices, they can be used as quantum simulators of unique many-body phenomena. In particular, we show that the decoupling of the nuclear spin from the electronic angular momentum can be used to implement many-body systems with an unprecedented degree of symmetry, characterized by the SU(N) group with N as large as 10. Moreover, the interplay of the nuclear spin with the electronic degree of freedom provided by a stable optically excited state should enable the study of physics governed by the spin–orbital interaction. Such systems may provide valuable insights into the physics of strongly correlated transition-metal oxides, heavy-fermion materials and spin-liquid phases.
Alternative URL (local restricted copy) - D. Chang, C. A. Regal, S. B. Papp, D. J. Wilson, J. Ye, O. Painter, H. J. Kimble, P. Zoller, Cavity optomechanics using an optically levitated nanosphere, PNAS 107, 1005, (2010-01-19), URL (ID: 708587) Toggle Abstract
Recently, remarkable advances have been made in coupling a number of high-Q modes of nano-mechanical systems to high-finesse optical cavities, with the goal of reaching regimes in which quantum behavior can be observed and leveraged toward new applications. To reach this regime, the coupling between these systems and their thermal environments must be minimized. Here we propose a novel approach to this problem, in which optically levitating a nano-mechanical system can greatly reduce its thermal contact, while simultaneously eliminating dissipation arising from clamping. Through the long coherence times allowed, this approach potentially opens the door to ground-state cooling and coherent manipulation of a single mesoscopic mechanical system or entanglement generation between spatially separate systems, even in room-temperature environments. As an example, we show that these goals should be achievable when the mechanical mode consists of the center-of-mass motion of a levitated nanosphere.
Alternative URL (local restricted copy) - Z. Idziaszek, T. Calarco, P. Zoller, Ion-assisted ground-state cooling of a trapped polar molecule, (2010-08-11), URL oai:arXiv.org:1008.1858v1 (ID: 717300) Toggle Abstract
We propose and analyze a scheme for sympathetic cooling of the translational motion of polar molecules in an optical lattice, interacting one by one with laser-cooled ions in a radio-frequency trap. The energy gap between the excitation spectra of the particles in their respective trapping potentials is bridged by means of a parametric resonance, provided by the additional modulation of the RF field. We analyze two scenarios: simultaneous laser cooling and energy exchange between the ion and the molecule, and a scheme when these two processes take place separately. We calculate the lowest final energy of the molecule and the cooling rate depending on the amplitude of the parametric modulation. For small parametric modulation, the dynamics can be solved analytically within the rotating wave approximation.
Alternative URL (local restricted copy) - H. Büchler, P. Zoller, I. Lesanovsky, M. Müller, H. Weimer, A Rydberg Quantum Simulator, Nature Physics 6, 382, (2010-03-14), URL doi:10.1038/nphys1614 (ID: 695077) Toggle Abstract
Following Feynman and as elaborated on by Lloyd, a universal quantum simulator (QS) is a controlled quantum device which reproduces the dynamics of any other many particle quantum system with short range interactions. This dynamics can refer to both coherent Hamiltonian and dissipative open system evolution. We investigate how laser excited Rydberg atoms in large spacing optical or magnetic lattices can provide an efficient implementation of a universal QS for spin models involving (high order) n-body interactions. This includes the simulation of Hamiltonians of exotic spin models involving n-particle constraints such as the Kitaev toric code, color code, and lattice gauge theories with spin liquid phases. In addition, it provides the ingredients for dissipative preparation of entangled states based on engineering n-particle reservoir couplings. The key basic building blocks of our architecture are efficient and high-fidelity n-qubit entangling gates via auxiliary Rydberg atoms, including a possible dissipative time step via optical pumping. This allows to mimic the time evolution of the system by a sequence of fast, parallel and high-fidelity n-particle coherent and dissipative Rydberg gates.
Alternative URL (local restricted copy) - B. Capogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Quantum Phases of Cold Polar Molecules in 2D Optical Lattices, Phys. Rev. Lett. 104, 125301, (2010-02-23), URL doi:10.1103/PhysRevLett.104.125301 (ID: 686428) Toggle Abstract
We study the quantum phases of hard-core bosonic polar molecules on a two-dimensional square lattice interacting via repulsive dipole-dipole interactions. In the limit of small tunneling, we find evidence for a devil’s staircase, where Mott solids appear at rational fillings of the lattice. For finite tunneling, we establish the existence of extended regions of parameters where the ground state is a supersolid, obtained by doping the solids either with particles or vacancies. We discuss the effects of finite temperature and finite-size confining potentials as relevant to experiments.
Alternative URL (local restricted copy) - S. Diehl, M. Baranov, A. J. Daley, P. Zoller, Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part I: Formal Developments, Phys. Rev. B 82, 064509, (2010-08-13), URL doi:10.1103/PhysRevB.82.064509 (ID: 716839) Toggle Abstract
We develop a quantum field theoretical framework to analytically study the three-body constrained Bose-Hubbard model beyond mean field and non-interacting spin wave approximations. It is based on an exact mapping of the constrained model to a theory with two coupled bosonic degrees of freedom with polynomial interactions, which have a natural interpretation as single particles and two-particle states. The procedure can be seen as a proper quantization of the Gutzwiller mean field theory. The theory is conveniently evaluated in the framework of the quantum effective action, for which the usual symmetry principles are now supplemented with a ``constraint principle'' operative on short distances. We test the theory via investigation of scattering properties of few particles in the limit of vanishing density, and we address the complementary problem in the limit of maximum filling, where the low lying excitations are holes and di-holes on top of the constraint induced insulator. This is the first of a sequence of two papers. The application of the formalism to the many-body problem, which can be realized with atoms in optical lattices with strong three-body loss, is performed in a related work [13].
Alternative URL (local restricted copy) - M. Wallquist, K. Hammerer, P. Zoller, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, J. Ye, H. Kimble, Single-atom cavity QED and optomicromechanics, Phys. Rev. A 81, 023816, (2010-02-18), URL doi:10.1103/PhysRevA.81.023816 (ID: 716968) Toggle Abstract
In a recent publication [K. Hammerer, M. Wallquist, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, P. Zoller, J. Ye, and H. J. Kimble, Phys. Rev. Lett. 103, 063005 (2009)] we have shown the possibility to achieve strong coupling of the quantized motion of a micron-sized mechanical system to the motion of a single trapped atom. In the proposed setup the coherent coupling between a SiN membrane and a single atom is mediated by the field of a high finesse cavity and can be much larger than the relevant decoherence rates. This makes the well-developed tools of cavity quantum electrodynamics with single atoms available in the realm of cavity optomechanics. In this article we elaborate on this scheme and provide detailed derivations and technical comments. Moreover, we give numerical as well as analytical results for a number of possible applications for transfer of squeezed or Fock states from atom to membrane as well as entanglement generation, taking full account of dissipation. In the limit of strong-coupling the preparation and verification of nonclassical states of a mesoscopic mechanical system is within reach.
Alternative URL (local restricted copy) - S. Diehl, M. Baranov, A. J. Daley, P. Zoller, Observability of Quantum Criticality and a Continuous Supersolid in Atomic Gases, Phys. Rev. Lett. 104, 165301, (2010-04-20), URL 10.1103/PhysRevLett.104.165301 (ID: 716766) Toggle Abstract
We analyze the Bose-Hubbard model with three-body onsite hardcore constraint, which stabilizes the system for an attractive interparticle interaction and allows, in particular, the formation of a superfluid phase of bosonic dimers. Our approach is based on an exact mapping of the constrained Hamiltonian to a theory of two coupled bosonic degrees of freedom. We demonstrate that the phase transition between atomic and dimer superfluidity is generically of the first order as a result of the Coleman-Weinberg phenomenon, while at unit filling we identify an Ising quantum critical point. At this filling, furthermore, a symmetry enhancement in the strong coupling limit leads to a continuous supersolid phase for deeply bound dimers, observable in experiments.
Alternative URL (local restricted copy) - S. Diehl, M. Baranov, A. J. Daley, P. Zoller, Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part II: Application to the Many-Body Problem, Phys. Rev. B 82, 064510, (2010-08-13), URL doi:10.1103/PhysRevB.82.064510 (ID: 716840) Toggle Abstract
We analyze the ground state phase diagram of attractive lattice bosons, which are stabilized by a three-body onsite hardcore constraint. A salient feature of this model is an Ising type transition from a conventional atomic superfluid to a dimer superfluid with vanishing atomic condensate. The study builds on an exact mapping of the constrained model to a theory of coupled bosons with polynomial interactions, proposed in a related paper [11]. In this framework, we focus by analytical means on aspects of the phase diagram which are intimately connected to interactions, and are thus not accessible in a mean field plus spin wave approach. First, we determine shifts in the mean field phase border, which are most pronounced in the low density regime. Second, the investigation of the strong coupling limit reveals the existence of a new collective mode, which emerges as a consequence of enhanced symmetries in this regime. Third, we show that the Ising type phase transition, driven first order via the competition of long wavelength modes at generic fillings, terminates into a true Ising quantum critical point in the vicinity of half filling.
Alternative URL (local restricted copy) - A. Kantian, A. J. Daley, P. Zoller, An eta-condensate of fermionic atom pairs via adiabatic state preparation, Phys. Rev. Lett. 104, (2010-05-19), URL doi:10.1103/PhysRevLett.104.240406 (ID: 716970) Toggle Abstract
We discuss how an $\\eta$-condensate, corresponding to an exact excited eigenstate of the Fermi-Hubbard model, can be produced with cold atoms in an optical lattice. Using time-dependent density matrix renormalisation group methods, we analyse a state preparation scheme beginning from a band insulator state in an optical superlattice. This state can act as an important test case, both for adiabatic preparation methods and the implementation of the many-body Hamiltonian, and measurements on the final state can be used to help detect associated errors.
Alternative URL (local restricted copy) - S. Diehl, A. Tomadin, A. Micheli, R. Fazio, P. Zoller, Dynamical Phase Transitions and Instabilities in Open Atomic Many-Body Systems, Phys. Rev. Lett. 105, 015702, (2010-07-01), URL doi:10.1103/PhysRevLett.105.015702 (ID: 717159) Toggle Abstract
We discuss an open driven-dissipative many-body system, in which the competition of unitary Hamiltonian and dissipative Liouvillian dynamics leads to a nonequilibrium phase transition. It shares features of a quantum phase transition in that it is interaction driven, and of a classical phase transition, in that the ordered phase is continuously connected to a thermal state. Within a generalized Gutzwiller approach which includes the description of mixed state density matrices, we characterize the complete phase diagram and the critical behavior at the phase transition approached as a function of time. We find a novel fluctuation induced dynamical instability, which occurs at long wavelength as a consequence of a subtle dissipative renormalization effect on the speed of sound.
Alternative URL (local restricted copy) - A. Glätzle, K. Hammerer, A. J. Daley, R. Blatt, P. Zoller, A single trapped atom in front of an oscillating mirror, Opt. Commun. 283, 758, (2010-03-15), URL doi:10.1016/j.optcom.2009.10.063 (ID: 717009) Toggle Abstract
We investigate the Wigner–Weisskopf decay of a two-level atom in front of an oscillating mirror. This work builds on and extends previous theoretical and experimental studies of the effects of a static mirror on spontaneous decay and resonance fluorescence. The spontaneously emitted field is inherently non-stationary due to the time-dependent boundary conditions and in order to study its spectral distribution we employ the operational definition of the spectrum of non-stationary light due to the seminal work by Eberly and Wódkiewicz. We find a rich dependence of this spectrum as well as of the effective decay rates and level shifts on the mirror–atom distance and on the amplitude and frequency of the mirror’s oscillations. The results presented here provide the basis for future studies of more complex setups, where the motion of the atom and/or the mirror are included as quantum degrees of freedom.
Alternative URL (local restricted copy) - G. Pupillo, A. Micheli, M. Boninsegni, I. Lesanovsky, P. Zoller, Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics, Phys. Rev. Lett. 104, 223002, (2010-06-01), URL (ID: 716985) Toggle Abstract
We discuss techniques to generate long-range interactions in a gas of ground state alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.
Alternative URL (local restricted copy)
- S. Montangero, R. Fazio, P. Zoller, G. Pupillo, Dipole oscillations of confined lattice bosons in one dimension, Phys. Rev. A 79, 041602(R), (2009-03-10), URL doi:10.1103/PhysRevA.79.041602 (ID: 620456) Toggle Abstract
We study the dynamics of a non-integrable system comprising interacting cold bosons trapped in an optical lattice in one-dimension by means of exact time-dependent numerical DMRG techniques. Particles are confined by a parabolic potential, and dipole oscillations are induced by displacing the trap center of a few lattice sites. Depending on the system parameters this motion can vary from undamped to overdamped. We study the dipole oscillations as a function of the lattice displacement, the particle density and the strength of interparticle interactions. These results explain the recent experiment C.D. Fertig et al., Phys. Rev. Lett. 94, 120403 (2005).
Alternative URL (local restricted copy) - A. V. Gorshkov, A. M. Rey, A. J. Daley, M. M. Boyd, J. Ye, P. Zoller, M. Lukin, Alkaline-Earth Atoms as Few-Qubit Quantum Registers, Phys. Rev. Lett. 102, 110503, (2009-03-18), URL doi:10.1103/PhysRevLett.102.110503 (ID: 644448) Toggle Abstract
We propose and analyze a novel approach to quantum information processing, in which multiple qubits can be encoded and manipulated using electronic and nuclear degrees of freedom associated with individual alkaline-earth-metal atoms trapped in an optical lattice. Specifically, we describe how the qubits within each register can be individually manipulated and measured with subwavelength optical resolution. We also show how such few-qubit registers can be coupled to each other in optical superlattices via conditional tunneling to form a scalable quantum network. Finally, potential applications to quantum computation and precision measurements are discussed.
Alternative URL (local restricted copy) - I. Lesanovsky, M. Müller, P. Zoller, Trap assisted creation of giant molecules and Rydberg-mediated coherent charge transfer in a Penning trap, Phys. Rev. A 79, 010701(R), (2009-01-14), URL doi:10.1103/PhysRevA.79.010701 (ID: 620459) Toggle Abstract
We study two ions confined in a Penning trap. We show that electronically highly excited states exist in which an electron is delocalized among the two ions forming a giant molecule of several micrometer size. At energies close to the top of the Coulomb barrier these molecular states can be regarded as superpositions of Rydberg states of individual ions. We illuminate the possibility to observe coherent charge transfer between the ions. Beyond a critical principal quantum number the electron can coherently tunnel through the Coulomb barrier to an adjacent doubly charged ion. The tunneling occurs on timescales on which the dynamics of the nuclei can be considered frozen and radiative decay can be neglected.
Alternative URL (local restricted copy) - A. J. Daley, J. Taylor, S. Diehl, M. Baranov, P. Zoller, Atomic three-body loss as a dynamical three-body interaction, Phys. Rev. Lett. 102, 040402, (2009-01-30), URL doi:10.1103/PhysRevLett.102.040402 (ID: 627388) Toggle Abstract
We discuss how large three-body loss of atoms in an optical lattice can give rise to effective hard-core three-body interactions. For bosons, in addition to the usual atomic superfluid, a dimer superfluid can then be observed for attractive two-body interactions. The non-equilibrium dynamics of preparation and stability of these phases are studied in 1D by combining time-dependent Density Matrix Renormalisation Group techniques with a quantum trajectories method.
Alternative URL (local restricted copy) - M. Müller, I. Lesanovsky, H. Weimer, H. Büchler, P. Zoller, Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency, Phys. Rev. Lett. 102, 170502, (2009-04-28), URL doi:10.1103/PhysRevLett.102.170502 (ID: 628410) Toggle Abstract
We demonstrate theoretically a parallelized C-NOT gate which allows to entangle a mesoscopic ensemble of atoms with a single control atom in a single step, with high fidelity and on a microsecond timescale. Our scheme relies on the strong and long-ranged interaction between Rydberg atoms triggering Electromagnetically Induced Transparency (EIT). By this we can robustly implement a conditional transfer of all ensemble atoms among two logical states, depending on the state of the control atom. We outline a many body interferometer which allows a comparison of two many-body quantum states by performing a measurement of the control atom.
Alternative URL (local restricted copy) - M. Ortner, A. Micheli, G. Pupillo, P. Zoller, Quantum Simulations of Extended Hubbard Models with Dipolar Crystals, New J. Phys. 11, 055045, (2009-05-14), URL doi: 10.1088/1367-2630/11/5/055045 (ID: 665436) Toggle Abstract
In this paper we study the realization of lattice models in mixtures of atomic and dipolar molecular quantum gases. We consider a situation where polar molecules form a self-assembled dipolar lattice, in which atoms or molecules of a second species can move and scatter. We describe the system dynamics in a master equation approach in the Brownian motion limit of slow particles and fast phonons, which we find appropriate for our system. In a wide regime of parameters, the reduced dynamics of the particles leads to physical realizations of extended Hubbard models with tuneable long-range interactions mediated by crystal phonons. This extends the notion of quantum simulation of strongly correlated systems with cold atoms and molecules to include phonon-dynamics, where all coupling parameters can be controlled by external fields.
Alternative URL (local restricted copy) - Y. Han, Y. Chan, W. Yi, A. J. Daley, S. Diehl, P. Zoller, L. Duan, Stabilization of the p-wave superfluid state in an optical lattice, Phys. Rev. Lett. 103, 070404, (2009-08-14), URL doi:10.1103/PhysRevLett.103.070404 (ID: 707070) Toggle Abstract
It is hard to stabilize the p-wave superfluid state of cold atomic gas in free space due to inelastic collisional losses. We consider the p-wave Feshbach resonance in an optical lattice, and show that it is possible to have a stable p-wave superfluid state where the multiatom collisional loss is suppressed through the quantum Zeno effect. We derive the effective Hamiltonian for this system, and calculate its phase diagram in a one-dimensional optical lattice. The results show rich phase transitions between the p-wave superfluid state and different types of insulator states induced either by interaction or by dissipation.
- A. Kantian, M. Dalmonte, S. Diehl, W. Hofstetter, P. Zoller, A. J. Daley, Atomic Color Superfluid via Three-Body Loss, Phys. Rev. Lett. 103, 240401, (2009-12-09), URL doi:10.1103/PhysRevLett.103.240401 (ID: 707092) Toggle Abstract
Large three-body loss rates in a three-component Fermi gas confined in an optical lattice can dynamically prevent atoms from tunneling so as to occupy a lattice site with three atoms. This effective constraint not only suppresses the occurrence of actual loss events, but stabilizes BCS-pairing phases by suppressing the formation of trions. We study the effect of the constraint on the many-body physics using bosonization and density matrix renormalization group techniques, and also investigate the full dissipative dynamics including loss for the example of 6Li.
Alternative URL (local restricted copy) - K. Hammerer, M. Wallquist, C. Genes, M. Ludwig, F. Marquardt, P. Treutlein, P. Zoller, J. Ye, H. J. Kimble, Strong coupling of a mechanical oscillator and a single atom, Phys. Rev. Lett. 103, 063005, (2009-08-06), URL doi:10.1103/PhysRevLett.103.063005 (ID: 680115) Toggle Abstract
We propose and analyze a setup to achieve strong coupling between a single trapped atom and a mechanical oscillator. The interaction between the motion of the atom and the mechanical oscillator is mediated by a quantized light field in a laser driven high-finesse cavity. In particular, we show that high fidelity transfer of quantum states between the atom and the mechanical oscillator is in reach for existing or near future experimental parameters. Our setup provides the basic toolbox for coherent manipulation, preparation and measurement of micro- and nanomechanical oscillators via the tools of atomic physics.
Alternative URL (local restricted copy) - K. Jähne, C. Genes, K. Hammerer, M. Wallquist, E. Polzik, P. Zoller, Cavity-assisted squeezing of a mechanical oscillator, Phys. Rev. A 79, 063819, (2009-06-11), URL doi:10.1103/PhysRevA.79.063819 (ID: 679748) Toggle Abstract
We investigate the creation of squeezed states of a vibrating membrane or a movable mirror in an opto-mechanical system. An optical cavity is driven by squeezed light and couples via radiation pressure to the membrane/mirror, effectively providing a squeezed heat-bath for the mechanical oscillator. Under the conditions of laser cooling to the ground state, we find an efficient transfer of squeezing with roughly 60% of light squeezing conveyed to the membrane/mirror (on a dB scale). We determine the requirements on the carrier frequency and the bandwidth of squeezed light. Beyond the conditions of ground state cooling, we predict mechanical squashing to be observable in current systems.
Alternative URL (local restricted copy) - D. Chang, J. D. Thompson, H. Park, V. Vuletic, P. Zoller, A. Zibrov, M. Lukin, Trapping and manipulation of isolated atoms using nanoscale plasmonic structures, Phys. Rev. Lett. 103, 123004, (2009-09-18), URL doi:10.1103/PhysRevLett.103.123004 (ID: 686216) Toggle Abstract
We propose and analyze a scheme to interface individual neutral atoms with nanoscale solid-state systems. The interface is enabled by optically trapping the atom via the strong near-field generated by a sharp metallic nanotip. We show that under realistic conditions, a neutral atom can be trapped with position uncertainties of just a few nanometers, and within tens of nanometers of other surfaces. Simultaneously, the guided surface plasmon modes of the nanotip allow the atom to be optically manipulated, or for fluorescence photons to be collected, with very high efficiency. Finally, we analyze the surface forces, heating and decoherence rates acting on the trapped atom.
Alternative URL (local restricted copy) - K. Hammerer, M. Aspelmeyer, E. Polzik, P. Zoller, Establishing Einstein-Poldosky-Rosen Channels between Nanomechanics and Atomic Ensembles, Phys. Rev. Lett. 102, 020501, (2009-01-12), URL doi:10.1103/PhysRevLett.102.020501 (ID: 637866) Toggle Abstract
We suggest interfacing nanomechanical systems via an optical quantum bus to atomic ensembles, for which means of high precision state preparation, manipulation, and measurement are available. This allows, in particular, for a quantum nondemolition Bell measurement, projecting the coupled system, atomic-ensemble–nanomechanical resonator, into an entangled EPR state. The entanglement is observable even for nanoresonators initially well above their ground states and can be utilized for teleportation of states from an atomic ensemble to the mechanical system.
- P. Zoller, M. Wallquist, K. Hammerer, P. Rabl, M. Lukin, Hybrid quantum devices and quantum engineering, Physica Scripta 014001, (2009-12-14), URL doi:10.1088/0031-8949/2009/T137/014001 (ID: 716806) Toggle Abstract
We discuss prospects of building hybrid quantum devices involving elements of atomic and molecular physics, quantum optics and solid-state elements with the attempt to combine advantages of the respective systems in compatible experimental setups. In particular, we summarize our recent work on quantum hybrid devices and briefly discuss recent ideas for quantum networks. These include interfacing of molecular quantum memory with circuit QED, and using nanomechanical elements strongly coupled to qubits represented by electronic spins, as well as single atoms or atomic ensembles.
Alternative URL (local restricted copy) - B. Capogrosso-Sansone, S. Wessel, H. Büchler, P. Zoller, G. Pupillo, Phase diagram of one-dimensional hard-core bosons with three-body interactions, Phys. Rev. B 79, 020503 (R), (2009-01-09), URL doi:10.1103/PhysRevB.79.020503 (ID: 603828) Toggle Abstract
We determine the phase diagram of a one-dimensional system of hard-core lattice bosons interacting via repulsive three-body interactions by analytic methods and extensive quantum Monte Carlo simulations. Such three-body interactions can be derived from a microscopic theory for polar molecules trapped in an optical lattice. Depending on the strength of the interactions and the particle density, we find superfluid and solid phases, the latter appearing at an unconventional filling of the lattice and displaying a coexistence of charge-density wave and bond orders
Alternative URL (local restricted copy)
- M. Müller, L. Liang, I. Lesanovsky, P. Zoller, Trapped Rydberg Ions: From Spin Chains to Fast Quantum Gates, New Journal of Physics 10, 093009, (2008-09-10), URL doi:10.1088/1367-2630/10/9/093009 (ID: 520204) Toggle Abstract
We study the quantum dynamics of trapped ions in Rydberg states, which have large electric dipole moments induced by the trapping fields. In the limit where the localization of the ion core is much smaller than the Rydberg orbit the dynamics of the system is determined by the interplay between large dipole-dipole energy shifts and strong tunable internal-state-dependent forces due to dipole-charge interactions. This provides a new tool for manipulating and entangling ions by strong interactions and on fast time scales.
Alternative URL (local restricted copy) - A. V. Gorshkov, P. Rabl, G. Pupillo, A. Micheli, P. Zoller, M. Lukin, H. Büchler, Suppression of Inelastic Collisions Between Polar Molecules With a Repulsive Shield, Phys. Rev. Lett. 101, 073201, (2008-08-14), URL doi:10.1103/PhysRevLett.101.073201 (ID: 582039) Toggle Abstract
We propose and analyze a technique that allows to suppress inelastic collisions and simultaneously enhance elastic interactions between cold polar molecules. The main idea is to cancel the leading dipole-dipole interaction with a suitable combination of static electric and microwave fields in such a way that the remaining van-der-Waals-type potential forms a three-dimensional repulsive shield. We analyze the elastic and inelastic scattering cross sections relevant for evaporative cooling of polar molecules and discuss the prospect for the creation of crystalline structures
Alternative URL (local restricted copy) - A. J. Daley, P. Zoller, B. Trauzettel, Andreev-like reflections with cold atoms, Physical Review Letters 100, 110404, (2008-03-20), URL doi:10.1103/PhysRevLett.100.110404 (ID: 530306) Toggle Abstract
We propose a setup in which Andreev-like reflections predicted for 1D transport systems could be observed time-dependently using cold atoms in a 1D optical lattice. Using time-dependent Density Matrix Renormalisation Group methods we analyse the wavepacket dynamics as a density excitation propagates across a boundary in the interaction strength. These phenomena exhibit good correspondence with predictions from Luttinger liquid models and could be observed in current experiments in the context of the Bose-Hubbard model.
Alternative URL (local restricted copy) - G. Pupillo, A. Griessner, A. Micheli, M. Ortner, Wang, Daw-Wei, P. Zoller, Cold Atoms and Molecules in Self-Assembled Dipolar Lattices, Phys. Rev. Lett. 100, 050402, (2008-02-05), URL doi:10.1103/PhysRevLett.100.050402 (ID: 519056) Toggle Abstract
We study the realization of lattice models, where cold atoms and molecules
move as extra particles in a dipolar crystal of trapped polar molecules. The
crystal is a self-assembled floating mesoscopic lattice structure with quantum
dynamics given by phonons. We show that within an experimentally accessible
parameter regime extended Hubbard models with tunable long-range
phonon-mediated interactions describe the effective dynamics of dressed
particles.
Alternative URL (local restricted copy) - W. Yi, A. J. Daley, G. Pupillo, P. Zoller, State-dependent, addressable subwavelength lattices with cold atoms, New Journal of Physics 10, 073015, (2008-07-08), URL doi:10.1088/1367-2630/10/7/073015 (ID: 582500) Toggle Abstract
We discuss how adiabatic potentials can be used to create addressable lattices on a subwavelength scale, which can be used as a tool for local operations and readout within a lattice substructure, while taking advantage of the faster timescales and higher energy and temperature scales determined by the shorter lattice spacing. For alkaline-earth-like atoms with non-zero nuclear spin, these potentials can be made state dependent, for which we give specific examples with $^{171}$Yb atoms. We discuss in detail the limitations in generating the lattice potentials, in particular non-adiabatic losses, and show that the loss rates can always be made exponentially small by increasing the laser power.
Alternative URL (local restricted copy) - S. Morrison, A. Kantian, A. J. Daley, H. Katzgraber, M. Lewenstein, H. Büchler, P. Zoller, Physical replicas and the Bose-glass in cold atomic gases, New J. Phys. 10, 073032, (2008-07-16), URL doi:10.1088/1367-2630/10/7/073032 (ID: 582497) Toggle Abstract
We study cold atomic gases in a disorder potential and analyse the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While, in general, these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose–Hubbard model and determine the overlap function within the perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes.
Alternative URL (local restricted copy) - T. Calarco, P. Grangier, A. Wallraff, P. Zoller, Quantum leaps in small steps, Nature Physics 4, 2, (2008-01-01), URL doi:10.1038/nphys818 (ID: 602500) Alternative URL (local restricted copy)
- A. V. Gorshkov, L. Jiang, M. Greiner, P. Zoller, M. Lukin, Coherent Quantum Optical Control with Subwavelength Resolution, Physical Review Letters 100, 093005, (2008-03-07), URL doi:10.1103/PhysRevLett.100.093005 (ID: 519563) Toggle Abstract
We suggest a new method for quantum optical control with nanoscale resolution. Our method allows for coherent far-field manipulation of individual quantum systems with spatial selectivity that is not limited by the wavelength of radiation and can, in principle, approach a few nanometers. The selectivity is enabled by the nonlinear atomic response, under the conditions of Electromagnetically Induced Transparency, to a control beam with intensity vanishing at a certain location. Practical performance of this technique and its potential applications to quantum information science with cold atoms, ions, and solid-state qubits are discussed.
Alternative URL (local restricted copy) - L. Jiang, G. Brennen, A. V. Gorshkov, K. Hammerer, M. Hafezi, E. Demler, M. Lukin, P. Zoller, Anyonic interferometry and protected memories in atomic spin lattices, Nature Physics 4, 482, (2008-04-20), URL doi:10.1038/nphys943 (ID: 538104) Toggle Abstract
Strongly correlated quantum systems can exhibit exotic behavior called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and have been proposed as candidates for naturally fault-tolerant quantum computation. Despite these remarkable properties, anyons have never been observed in nature directly. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations.
Alternative URL (local restricted copy) - A. J. Daley, M. M. Boyd, J. Ye, P. Zoller, Quantum Computing with Alkaline-Earth-Metal Atoms, Phys. Rev. Lett. 101, 170504, (2008-10-23), URL doi:10.1103/PhysRevLett.101.170504 (ID: 606889) Toggle Abstract
We present a complete scheme for quantum information processing using the unique features of alkaline earth atoms. We show how two completely independent lattices can be formed for the $^1$S$_0$ and $^3$P$_0$ states, with one used as a storage lattice for qubits encoded on the nuclear spin, and the other as a transport lattice to move qubits and perform gate operations. We discuss how the $^3$P$_2$ level can be used for addressing of individual qubits, and how collisional losses from metastable states can be used to perform gates via a lossy blockade mechanism.
Alternative URL (local restricted copy) - B. Kraus, H. Büchler, S. Diehl, A. Kantian, A. Micheli, P. Zoller, Preparation of Entangled States by Quantum Markov Processes, Phys. Rev. A 78, 042307, (2008-05-02), URL doi:10.1103/PhysRevA.78.042307 (ID: 576234) Toggle Abstract
We investigate the possibility of using a dissipative process to prepare a quantum system in a desired state. We derive for any multipartite pure state a dissipative process for which this state is the unique stationary state and solve the corresponding master equation analytically. For certain states, such as the cluster states, we use this process to show that the jump operators can be chosen quasilocally, i.e. they act nontrivially only on a few, neighboring qubits. Furthermore, the relaxation time of this dissipative process is independent of the number of subsystems. We demonstrate the general formalism by considering arbitrary matrix-product states or projected entangled pair states. In particular, we show that the ground state of the Affleck-Kennedy-Lieb-Tasaki model can be prepared employing a quasi-local dissipative process.
- S. Diehl, A. Micheli, A. Kantian, B. Kraus, H. Büchler, P. Zoller, Quantum States and Phases in Driven Open Quantum Systems with Cold Atoms, Nature Physics 4, 878, (2008-09-07), URL doi:10.1038/nphys1073 (ID: 576233) Toggle Abstract
An open quantum system, whose time evolution is governed by a master equation, can be driven into a given pure quantum state by an appropriate design of the system-reservoir coupling. This points out a route towards preparing many body states and non-equilibrium quantum phases by quantum reservoir engineering. Here we discuss in detail the example of a \emph{driven dissipative Bose Einstein Condensate} of bosons and of paired fermions, where atoms in an optical lattice are coupled to a bath of Bogoliubov excitations via the atomic current representing \emph{local dissipation}. In the absence of interactions the lattice gas is driven into a pure state with long range order. Weak interactions lead to a weakly mixed state, which in 3D can be understood as a depletion of the condensate, and in 1D and 2D exhibits properties reminiscent of a Luttinger liquid or a Kosterlitz-Thouless critical phase at finite temperature, with the role of the ``finite temperature'' played by the interactions.
- M. Wallquist, P. Rabl, M. Lukin, P. Zoller, Theory of cavity-assisted microwave cooling of polar molecules, New Journal of Physics 10, 063005, (2008-06-04), URL doi:10.1088/1367-2630/10/6/063005 (ID: 567588) Toggle Abstract
We analyze cavity-assisted cooling schemes for polar molecules in the microwave domain, where molecules are excited on a rotational transition and energy is dissipated via strong interactions with a lossy stripline cavity, as recently proposed by André et al 2006 Nat. Phys. 2 636. We identify the dominant cooling and heating mechanisms in this setup and study cooling rates and final temperatures in various parameter regimes. In particular, we analyze the effects of a finite environment temperature on the cooling efficiency, and find minimal temperature and optimized cooling rate in the strong drive regime. Further, we discuss the trade-off between efficiency of cavity cooling and robustness with respect to ubiquitous imperfections in a realistic experimental setup, such as anharmonicity of the trapping potential.
Alternative URL (local restricted copy)
- P. Zoller, Mesoscopic superpositions of quantum phases and quantum states via Rydberg interactions, Symposium of the Jack Dodd-Dan Walls Centre for Photonics and Ultra-Cold Atmos (Queenstown, Neuseeland, 2008-12-09),
(2008-12-11), (ID: 637754)
- P. Zoller, Cold atoms as a driven open quantum optical system, Quantum Noise in Correlated Systems (Rehovot, Israel, 2008-01-05), URL
(2008-01-06), (ID: 551015) Toggle Abstract
We consider state preparation of a many body system of cold atoms via driven dissipative processes [1]. While the standard scenario of cold atom physics prepares interesting many body states as ground state of a Hamiltonian (i.e. a state of thermal equilibrium obtained at very low temperatures), we are interested in a situation where we engineer the reservoir couplings so that we "cool" the system to a particular
(pure) many body state in dynamical equilibrium between driving and dissipation. We will formulate this problem along the lines of quantum optics, which considers the dynamics of open quantum systems as a quantum Markov process, adopting the language of stochastic Schrödinger and master equations.
As particular example we consider cold atoms in an optical lattice, which can be excited by lasers to higher Bloch bands, and which are coupled to the Bogoliubov excitations of a Bose Einstein condensate (of a second atomic species) representing a bath. We will write down and carefully establish the validity of a master equation for this cold atom dynamics involving local dissipative couplings, which in steady state and in the limit of strong driving prepares bosonic atoms in a pure state of long range order, i.e. in a dissipatively driven BEC. For finite driving we obtain a mixed state with "effective temperature" determined by the competition between driving and atomic collisional interactions.
Finally, we provide an outlook how to engineer other classes of many body states as the dynamical equilibrium of a driven dissipative system.
[1] A. Micheli, H.P. Buchler, S. Diehl and P. Zoller, in preparation
- P. Zoller, Condensed matter physics and quantum information processing with cold, Cold Atom Theory Workshop (Queenstown, Neuseeland, 2008-12-12),
(2008-12-12), (ID: 637758) Toggle Abstract
We discuss prospects offered by cold polar molecules in the context of
implementing strongly interacting condensed matter systems and quantum
information processing. In the talk we will first give a general
introduction and survey of basic ideas, and then focus on particular
examples including realization of general 2D spin models with
molecules in optical lattices, the formation of 2D self-assembled
lattices of polar molecules, and molecular ensembles as quantum memory
- P. Zoller, Quantum states and phases in driven open quantum systems with cold atoms, Castu Cold Atom Conference (Beijing, China, 2008-10-20), URL
(2008-10-20), (ID: 623020)
- P. Zoller, Quantum information and non-equlibrium condensed matter physics with cold atoms, ICAP 2008 (Storrs, USA, 2008-07-27), URL
(2008-07-28), (ID: 620795)
- P. Zoller, Quantum Information with Driven Dissipative Quantum Optical Systems, GRC on Quantum Information Science (Big Sky Resort, Montana, USA, 2008-08-31), URL
(2008-09-04), (ID: 620029)
- P. Zoller, Many-body dynamics in driven dissipative systems, Theory of Quantum Gases and Quantum Coherence, 4th International Workshop (Grenoble, France, 2008-06-03), URL
(2008-06-06), (ID: 591800) Toggle Abstract
Quantum optics typically considers driven open quantum system, where a system of interest is driven by an external field and coupled to an environment inducing non-equilibrium dynamics, with time evolution described by a master equation. For long times, such a system will approach a dynamical steady state, which in general will be a mixed state. However, this steady state can also be a pure state: this is achieved by an appropriate design of the system-reservoir couplings, as reflected in the "quantum jump operators" (or Lindblad operators) in the dissipative terms of a master equation, in combination with a proper system Hamiltonian. Here we are interested in extending driven dissipative state preparation of quantum states to the case of many body systems. This is of interest both as a novel way of preparing entangled states in quantum information, and suggests a new form of non-equilibrium condensed matter physics. In this talk we will focus on the latter part, including topics like (i) physical realization of reservoir engineering with cold atoms, (ii) a characterization of non-equilibrium condensed matter phases of driven dissipative systems, including phase transitions, and (iii) questions related to the dynamics of approaching the steady state.
- P. Zoller, Opto-nanomechanics atomic-ensemble quantum interfaces, Workshop on Quantum Phenomena and Information: From Atomic to Mesoscopic Systems (Trieste, Italy, 2008-05-05), URL
(2008-05-12), (ID: 582874)
- P. Rabl, P. Zoller, Molecular Dipolar Crystals as High Fidelity Quantum Memory for Hybrid Quantum Computing, Phys. Rev. A 76, 042308, (2007-10-04), URL doi:10.1103/PhysRevA.76.042308 (ID: 494007) Toggle Abstract
We study collective excitations of rotational and spin states of an ensemble of polar molecules, which are prepared in a dipolar crystalline phase, as a candidate for a high fidelity quantum memory. While dipolar crystals are formed in the high density limit of cold clouds of polar molecules under 1D and 2D trapping conditions, the crystalline structure protects the molecular qubits from detrimental effects of short range collisions. We calculate the lifetime of the quantum memory by identifying the dominant decoherence mechanisms, and estimate their effects on gate operations, when a molecular ensemble qubit is transferred to a superconducting strip line cavity (circuit QED). In the case rotational excitations coupled by dipole-dipole interactions we identify phonons as the main limitation of the life time of qubits. We study specific setups and conditions, where the coupling to the phonon modes is minimized. Detailed results are presented for a 1D dipolar chain.
- Z. Idziaszek, T. Calarco, P. Zoller, Controlled collisions of a single atom and ion guided by movable trapping potentials, Phys. Rev. A 76, 033409, (2007-09-19), URL doi:10.1103/PhysRevA.76.033409 (ID: 470101) Toggle Abstract
We consider a system composed of a trapped atom and a trapped ion. The ion charge induces in the atom an electric dipole moment, which attracts it with an r^{-4} dependence at large distances. In the regime considered here, the characteristic range of the atom-ion interaction is comparable or larger than the characteristic size of the trapping potential, which excludes the application of the contact pseudopotential. The short-range part of the interaction is described in the framework of quantum-defect theory, by introducing some short-range parameters, which can be related to the s-wave scattering length. When the separation between traps is changed we observe trap-induced shape resonances between molecular bound states and vibrational states of the external trapping potential. Our analysis is extended to quasi-one-dimensional geometries, when the scattering exhibit confinement-induced resonances, similar to the ones studied before for short-range interactions. For quasi-one-dimensional systems we investigate the effects of coupling between the center of mass and relative motion, which occurs for different trapping frequencies of atom and ion traps. Finally, we show how the two types of resonances can be employed for quantum state control and spectroscopy of atom-ion molecules.
Alternative URL (local restricted copy) - A. Kantian, A. J. Daley, P. Törmä, P. Zoller, Atomic lattice excitons: from condensates to crystals, New Journal of Physics 9, 407, (2007-11-13), URL doi:10.1088/1367-2630/9/11/407 (ID: 514263) Toggle Abstract
We discuss atomic lattice excitons (ALEs), bound particle-hole pairs formed by fermionic atoms in two bands of an optical lattice. Such a system provides a clean setup to study fundamental properties of excitons, ranging from condensation to exciton crystals (which appear for a large effective mass ratio between particles and holes). Using both mean-field treatments and 1D numerical computation, we discuss the properities of ALEs under varying conditions, and discuss in particular their preparation and measurement.
Alternative URL (local restricted copy) - H. Büchler, E. Demler, M. Lukin, A. Micheli, N. Prokofev, G. Pupillo, P. Zoller, Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential, Phys. Rev. Lett. 98, 060404, (2007-02-08), URL doi:10.1103/PhysRevLett.98.060404 (ID: 376275) Toggle Abstract
We discuss techniques to tune and shape the long-range part of the interaction potentials in quantum gases of bosonic polar molecules by dressing rotational excitations with static and microwave fields. This provides a novel tool towards engineering strongly correlated quantum phases in combination with low-dimensional trapping geometries. As an illustration, we discuss the 2D superfluid-crystal quantum phase transition for polar molecules interacting via an electric-field-induced dipole-dipole potential.
Alternative URL (local restricted copy) - S. Tewari, S. D. Sarma, C. Nayak, C. Zhang, P. Zoller, Quantum Computation using Vortices and Majorana Zero Modes of a px+ipy Superfluid of Fermionic Cold Atoms, Phys. Rev. Lett. 98, 010506, (2007-01-05), URL doi:10.1103/PhysRevLett.98.010506 (ID: 436036) Toggle Abstract
We propose to use the recently predicted two-dimensional “weak-pairing” px+ipy superfluid state of fermionic cold atoms as a platform for topological quantum computation. In the core of a vortex, this state supports a zero-energy Majorana mode, which moves to finite energy in the corresponding topologically trivial “strong-pairing” state. By braiding vortices in the “weak-pairing” state, unitary quantum gates can be applied to the Hilbert space of Majorana zero modes. For readout of the topological qubits, we propose realistic schemes suitable for atomic superfluids.
Alternative URL (local restricted copy) - A. Griessner, A. J. Daley, S. Clark, D. Jaksch, P. Zoller, Dissipative dynamics of atomic Hubbard models coupled to a phonon bath: Dark state cooling of atoms within a Bloch band of an optical lattice, New Journal of Physics 9, 44, (2007), URL doi:10.1088/1367-2630/9/2/044 (ID: 428626) Toggle Abstract
We analyse a laser assisted sympathetic cooling scheme for atoms within the lowest Bloch band of an optical lattice. This scheme borrows ideas from sub-recoil laser cooling, implementing them in a new context in which the atoms in the lattice are coupled to a Bose–Einstein condensate (BEC) reservoir. In this scheme, excitation of atoms between Bloch bands replaces the internal structure of atoms in normal laser cooling, and spontaneous emission of photons is replaced by creation of excitations in the BEC reservoir. We analyse the cooling process for many bosons and fermions, and obtain possible temperatures corresponding to a small fraction of the Bloch band width within our model. This system can be seen as a novel realisation of a many-body open quantum system.
Alternative URL (local restricted copy) - G. Brennen, A. Micheli, P. Zoller, Designing spin-1 lattice models using polar molecules, New Journal of Physics 9, 138, (2007-05-18), URL doi:10.1088/1367-2630/9/5/138 (ID: 430363) Toggle Abstract
We describe how to design a large class of always on spin-1 interactions between polar molecules trapped in an optical lattice. The spin degrees of freedom correspond to the hyperfine levels of a ro-vibrational ground state molecule. Interactions are induced using a microwave field to mix ground states in one hyperfine manifold with the spin entangled dipole-dipole coupled excited states. Using multiple fields anistropic models in one, two, or three dimensions, can be built with tunable spatial range. An illustrative example in one dimension is the generalized Haldane model, which at a specific parameter has a gapped valence bond solid ground state. The interaction strengths are large compared to decoherence rates and should allow for probing the rich phase structure of strongly correlated systems, including dimerized and gapped phases.
Alternative URL (local restricted copy) - A. Micheli, G. Pupillo, H. Büchler, P. Zoller, Cold polar molecules in 2D traps: Tailoring interactions with external fields for novel quantum phases, Phys. Rev. A 76, 043604, (2007-10-03), URL doi:10.1103/PhysRevA.76.043604 (ID: 460560) Toggle Abstract
We discuss techniques to engineer effective long-range interactions between polar molecules using external static electric and microwave fields. We consider a setup where molecules are trapped in a two-dimensional pancake geometry by a far-off-resonance optical trap, which ensures the stability of the dipolar collisions. We detail how to modify the shape and the strength of the long-range part of interaction potentials, which can be utilized to realize interesting quantum phases in the context of cold molecular gases.
Alternative URL (local restricted copy) - H. Büchler, A. Micheli, P. Zoller, Three-body interactions with cold polar molecules, Nature Physics 3, 726, (2007-07-22), URL doi:10.1038/nphys678 (ID: 462909) Toggle Abstract
We show that polar molecules driven by microwave fields give naturally rise to strong three-body interactions, while the two-particle interaction can be independently controlled and even switched off. The derivation of these effective interaction potentials is based on a microscopic understanding of the underlying molecular physics, and follows from a well controlled and systematic expansion into many-body interaction terms. For molecules trapped in an optical lattice, we show that these interaction potentials give rise to Hubbard models with strong nearest-neighbor two-body and three-body interaction. As an illustration, we study the one-dimensional Bose-Hubbard model with dominant three-body interaction and derive its phase diagram.
Alternative URL (local restricted copy)
- P. Rabl, D. DeMille, J. Doyle, M. Lukin, R. J. Schoelkopf, P. Zoller, Hybrid Quantum Processors: molecular ensembles as quantum memory for solid state circuits, Phys. Rev. Lett. 97, 033003, (2006-07-21), URL doi:10.1103/PhysRevLett.97.033003 (ID: 353814) Toggle Abstract
We investigate a hybrid quantum circuit where ensembles of cold polar molecules serve as long-lived quantum memories and optical interfaces for solid state quantum processors. The quantum memory realized by collective spin states (ensemble qubit) is coupled to a high-Q stripline cavity via microwave Raman processes. We show that, for convenient trap-surface distances of a few µm, strong coupling between the cavity and ensemble qubit can be achieved. We discuss basic quantum information protocols, including a swap from the cavity photon bus to the molecular quantum memory, and a deterministic two qubit gate. Finally, we investigate coherence properties of molecular ensemble quantum bits.
Alternative URL (local restricted copy) - A. Micheli, G. Brennen, P. Zoller, A toolbox for lattice spin models with polar molecules, Nature Physics 2, 341, (2006-05-00), URL doi:10.1038/nphys287 (ID: 313100) Toggle Abstract
There is growing interest in states of matter with topological order. These are characterized by highly stable ground states robust to perturbations that preserve the topology, and which support excitations with so-called anyonic statistics. Topologically ordered states can arise in two-dimensional lattice-spin models, which were proposed as the basis for a new class of quantum computation. Here, we show that the relevant hamiltonians for such spin lattice models can be systematically engineered with polar molecules stored in optical lattices, where the spin is represented by a single-valence electron of a heteronuclear molecule. The combination of microwave excitation with dipole–dipole interactions and spin–rotation couplings enables building a complete toolbox for effective two-spin interactions with designable range, spatial anisotropy and coupling strengths significantly larger than relevant decoherence rates. Finally, we illustrate two models: one with an energy gap providing for error-resilient qubit encoding, and another leading to topologically protected quantum memory.
Alternative URL (local restricted copy) - S. Trebst, U. Schollwöck, M. Troyer, P. Zoller, d-Wave Resonating Valence Bond States of Fermionic Atoms in Optical Lattices, Phys. Rev. Lett. 96, 250402, (2006-06-30), URL doi:10.1103/PhysRevLett.96.250402 (ID: 372594) Toggle Abstract
We study controlled generation and measurement of superfluid d-wave resonating valence bond (RVB) states of fermionic atoms in 2D optical lattices. Starting from loading spatial and spin patterns of atoms in optical superlattices as pure quantum states from a Fermi gas, we adiabatically transform this state to an RVB state by a change of the lattice parameters. Results of exact time-dependent numerical studies for ladders systems are presented, suggesting generation of RVB states on a time scale smaller than typical experimental decoherence times.
Alternative URL (local restricted copy) - A. Griessner, A. J. Daley, S. Clark, D. Jaksch, P. Zoller, Dark state cooling of atoms by superfluid immersion, Phys. Rev. Lett. 97, 220403, (2006-12-04), URL doi:10.1103/PhysRevLett.97.220403 (ID: 375452) Toggle Abstract
We propose and analyze a scheme to cool atoms in an optical lattice to ultralow temperatures within a Bloch band and away from commensurate filling. The protocol is inspired by ideas from dark-state laser cooling but replaces electronic states with motional levels and spontaneous emission of photons by emission of phonons into a Bose-Einstein condensate, in which the lattice is immersed. In our model, achievable temperatures correspond to a small fraction of the Bloch bandwidth and are much lower than the reservoir temperature. This is also a novel realization of an open quantum optical system, where known tools are combined with new ideas involving cooling via a reservoir.
Alternative URL (local restricted copy) - P. Bushev, D. Rotter, A. Wilson, F. Dubin, C. Becher, J. Eschner, R. Blatt, V. Steixner, P. Rabl, P. Zoller, Feedback cooling of a single trapped ion, Physical Review Letters 96, 043003, (2006-02-03), URL doi:10.1103/PhysRevLett.96.043003 (ID: 332288) Toggle Abstract
Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electromechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical master equation.
- K. Winkler, G. Thalhammer, F. Lang, R. Grimm, J. Hecker Denschlag, A. J. Daley, A. Kantian, H. Büchler, P. Zoller, Repulsively bound atom pairs in an optical lattice, Nature 441, 853, (2006-06-15), URL doi:10.1038/nature04918 (ID: 371157) Toggle Abstract
Throughout physics, stable composite objects are usually formed by way of attractive forces, which allow the constituents to lower their energy by binding together. Repulsive forces separate particles in free space. However, in a structured environment such as a periodic potential and in the absence of dissipation, stable composite objects can exist even for repulsive interactions. Here we report the observation of such an exotic bound state, which comprises a pair of ultracold rubidium atoms in an optical lattice. Consistent with our theoretical analysis, these repulsively bound pairs exhibit long lifetimes, even under conditions when they collide with one another. Signatures of the pairs are also recognized in the characteristic momentum distribution and through spectroscopic measurements. There is no analogue in traditional condensed matter systems of such repulsively bound pairs, owing to the presence of strong decay channels. Our results exemplify the strong correspondence between the optical lattice physics of ultracold bosonic atoms and the Bose–Hubbard model—a link that is vital for future applications of these systems to the study of strongly correlated condensed matter and to quantum information.
Alternative URL (local restricted copy) - M. Cozzini, T. Calarco, A. Recati, P. Zoller, Fast Rydberg gates without dipole blockade via quantum control, Opt. Com. 264, 375, (2006-08-15), URL (ID: 313117) Toggle Abstract
We propose a scheme for controlling interactions between Rydberg-excited neutral atoms in order to perform a fast high-fidelity quantum gate. Unlike dipole-blockade mechanisms already found in the literature, we drive resonantly the atoms with a state-dependent excitation to Rydberg levels, and we exploit the resulting dipole–dipole interaction to induce a controlled atomic motion in the trap, in a similar way as discussed in recent ion-trap quantum computing proposals. This leads atoms to gain the required gate phase, which turns out to be a combination of a dynamic and a geometrical contribution. The fidelity of this scheme is studied including small anharmonicity and temperature effects, with promising results for reasonably achievable experimental parameters.
Alternative URL (local restricted copy) - André, A, D. DeMille, J. Doyle, M. Lukin, S. E. Maxwell, P. Rabl, R. J. Schoelkopf, P. Zoller, A coherent all-electrical interface between polar molecules and mesoscopic superconducting resonators, Nature Physics 2, 636, (2006-08-27), URL doi:10.1038/nphys386 (ID: 363758) Toggle Abstract
Building a scalable quantum processor requires coherent control and preservation of quantum coherence in a large-scale quantum system. Mesoscopic solid-state systems such as Josephson junctions and quantum dots feature robust control techniques using local electrical signals and self-evident scaling; however, in general the quantum states decohere rapidly. In contrast, quantum optical systems based on trapped ions and neutral atoms exhibit much better coherence properties, but their miniaturization and integration with electrical circuits remains a challenge. Here we describe methods for the integration of a single-particle system—an isolated polar molecule—with mesoscopic solid-state devices in a way that produces robust, coherent, quantum-level control. Our setup provides a scalable cavity-QED-type quantum computer architecture, where entanglement of distant qubits stored in long-lived rotational molecular states is achieved via exchange of microwave photons.
Alternative URL (local restricted copy)
- U. Dorner, T. Calarco, P. Zoller, A. Browaeys, P. Grangiere, Quantum logic via optimal control in holographic dipole traps, J. Opt. B: Quantum Semiclass. Opt. 7, 341-346, (2005), URL doi:10.1088/1464-4266/7/10/020 (ID: 308221) Toggle Abstract
We propose a scheme for quantum logic with neutral atoms stored in an array of holographic dipole traps where the positions of the atoms can be rearranged by using holographic optical tweezers. In particular, this allows for the transport of two atoms to the same well where an external control field is used to perform gate operations via the molecular interaction between the atoms. We show that optimal control techniques allow for the fast implementation of the gates with high fidelity.
Alternative URL (local restricted copy) - A. Micheli, P. Zoller, A Single Atom Mirror for 1D Atomic Lattice Gases, Phys. Rev. A 73, 043613, (2005-04-20), URL doi:10.1103/PhysRevA.73.043613 (ID: 313116) Toggle Abstract
We propose a scheme utilizing quantum interference to control the transport of atoms in a 1D optical lattice by a single impurity atom. The two internal state of the impurity represent a spin-1/2 (qubit), which in one spin state is perfectly transparent to the lattice gas, and in the other spin state acts as a single atom mirror, confining the lattice gas. This allows to ``amplify'' the state of the qubit, and provides a single-shot quantum non-demolition measurement of the state of the qubit. We derive exact analytical expression for the scattering of a single atom by the impurity, and give approximate expressions for the dynamics a gas of many interacting bosonic of fermionic atoms.
Alternative URL (local restricted copy) - D. Jaksch, P. Zoller, The cold atom Hubbard toolbox, Annals of Physics 315, 52-79, (2005), URL doi:10.1016/j.aop.2004.09.010 (ID: 308231) Toggle Abstract
We review recent theoretical advances in cold atom physics concentrating on strongly correlated cold atoms in optical lattices. We discuss recently developed quantum optical tools for manipulating atoms and show how they can be used to realize a wide range of many body Hamiltonians. Then, we describe connections and differences to condensed matter physics and present applications in the fields of quantum computing and quantum simulations. Finally, we explain how defects and atomic quantum dots can be introduced in a controlled way in optical lattice systems.
Alternative URL (local restricted copy) - J. Taylor, H. Engel, W. Dür, A. Yacoby, C. M. Marcus, P. Zoller, M. Lukin, Fault-tolerant architecture for quantum computation using electrically controlled semiconductor spins, Nature Physics 1, 177-183, (2005), URL doi:10.1038/nphys174 (ID: 308201) Toggle Abstract
Information processing using quantum systems provides new paradigms for computation and communication and may yield insights into our understanding of the limits of quantum mechanics. However, realistic systems are never perfectly isolated from their environment, hence all quantum operations are subject to errors. Realization of a physical system for processing of quantum information that is tolerant of errors is a fundamental problem in quantum science and engineering. Here, we develop an architecture for quantum computation using electrically controlled semiconductor spins by extending the Loss–DiVincenzo scheme and by combining actively protected quantum memory and long-distance coupling mechanisms. Our approach is based on a demonstrated encoding of qubits in long-lived two-electron states, which immunizes qubits against the dominant error from hyperfine interactions. We develop a universal set of quantum gates compatible with active error suppression for these encoded qubits and an effective long-range interaction between the qubits by controlled electron transport. This approach yields a scalable architecture with favourable error thresholds for fault-tolerant operation, consistent with present experimental parameters.
Alternative URL (local restricted copy) - A. Griessner, A. J. Daley, D. Jaksch, P. Zoller, Fault-tolerant dissipative preparation of atomic quantum registers with fermions, Phys. Rev. A 72, 032332, (2005), URL doi:10.1103/PhysRevA.72.032332 (ID: 308207) Toggle Abstract
We propose a fault-tolerant loading scheme to produce an array of fermions in an optical lattice of the high fidelity required for applications in quantum-information processing and the modeling of strongly correlated systems. A cold reservoir of fermions plays a dual role as a source of atoms to be loaded into the lattice via a Raman process and as a heat bath for sympathetic cooling of lattice atoms. Atoms are initially transferred into an excited motional state in each lattice site and then decay to the motional ground state, creating particle-hole pairs in the reservoir. Atoms transferred into the ground motional level are no longer coupled back to the reservoir, and doubly occupied sites in the motional ground state are prevented by Pauli blocking. This scheme has strong conceptual connections with optical pumping and can be extended to load high-fidelity patterns of atoms.
Alternative URL (local restricted copy) - K. Osterloh, M. Baig, L. Santos, P. Zoller, M. Lewenstein, Cold Atoms in Non-Abelian Gauge Potentials: From the Hofstadter "Moth" to Lattice Gauge Theory, Phys. Rev. Lett. 95, 010403, (2005), URL doi:10.1103/PhysRevLett.95.010403 (ID: 308223) Toggle Abstract
We demonstrate how to create artificial external non-Abelian gauge potentials acting on cold atoms in optical lattices. The method employs atoms with k internal states, and laser assisted state sensitive tunneling, described by unitary k×k matrices. The single-particle dynamics in the case of intense U(2) vector potentials lead to a generalized Hofstadter butterfly spectrum which shows a complex mothlike structure. We discuss the possibility to realize non-Abelian interferometry (Aharonov-Bohm effect) and to study many-body dynamics of ultracold matter in external lattice gauge fields.
- A. J. Daley, S. Clark, D. Jaksch, P. Zoller, Numerical analysis of coherent many-body currents in a single atom transistor, Phys. Rev. A 72, 043618, (2005), URL doi:10.1103/PhysRevA.72.043618 (ID: 308211) Toggle Abstract
We study the dynamics of many atoms in the recently proposed single-atom-transistor setup [A. Micheli, A. J. Daley, D. Jaksch, and P. Zoller, Phys. Rev. Lett. 93, 140408 (2004)] using recently developed numerical methods. In this setup, a localized spin-1/2 impurity is used to switch the transport of atoms in a one-dimensional optical lattice: in one state the impurity is transparent to probe atoms, but in the other acts as a single-atom mirror. We calculate time-dependent currents for bosons passing the impurity atom, and find interesting many-body effects. These include substantially different transport properties for bosons in the strongly interacting (Tonks) regime when compared with fermions, and an unexpected decrease in the current when weakly interacting probe atoms are initially accelerated to a nonzero mean momentum. We also provide more insight into the application of our numerical methods to this system, and discuss open questions about the currents approached by the system on long time scales.
Alternative URL (local restricted copy) - J. J. García-Ripoll, P. Zoller, J. I. Cirac, Quantum information processing with cold atoms and trapped ions, J. Phys. B: At. Mol. Opt. Phys. 38, 567-578, (2005), URL doi:10.1088/0953-4075/38/9/008 (ID: 308228) Toggle Abstract
This paper summarizes some important achievements of quantum information processing with trapped ions or neutral atoms. In particular, we describe the storage of information and realization of two-qubit gates with ions, as well as the creation of entanglement and quantum simulation with cold atoms in optical lattices.
Alternative URL (local restricted copy) - P. Zoller, T. Beth, D. Binosi, R. Blatt, H. J. Briegel, D. Bruss, T. Calarco, J. I. Cirac, D. Deutsch, J. Eisert, A. Ekert, C. Fabre, N. Gisin, P. Grangiere, M. Grassl, S. Haroche, A. Imamoglu, A. Karlson, J. Kempe, L. Louwenhofen, S. Kröll, G. Leuchs, M., Quantum information processing and communication, Eur. Phys. J. D 36/2, 203 - 228, (2005-11-01), URL doi:10.1140/epjd/e2005-00251-1 (ID: 375863) Toggle Abstract
We present an excerpt of the document “Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe”, which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European Commission, http://www.cordis.lu/ist/fet/qipc-sr.htm). This document has been elaborated, following a former suggestion by FET, by a committee of QIPC scientists to provide input towards the European Commission for the preparation of the Seventh Framework Program. Besides being a document addressed to policy makers and funding agencies (both at the European and national level), the document contains a detailed scientific assessment of the state-of-the-art, main research goals, challenges, strengths, weaknesses, visions and perspectives of all the most relevant QIPC sub-fields, that we report here. Dedicated to the memory of Prof. Th. Beth, one of the pioneers of QIPC, whose contributions have had a significant scientific impact on the development as well as on the visibility of a field that he enthusiastically helped to shape since its early days.
- J. Taylor, W. Dür, P. Zoller, A. Yacoby, C. M. Marcus, M. Lukin, Solid-State Circuit for Spin Entanglement Generation and Purification, Phys. Rev. Lett. 94, 236803, (2005), URL doi:10.1103/PhysRevLett.94.236803 (ID: 308222) Toggle Abstract
We show how realistic charge manipulation and measurement techniques, combined with the exchange interaction, allow for the robust generation and purification of four-particle spin entangled states in electrically controlled semiconductor quantum dots. The generated states are immunized to the dominant sources of noise via a dynamical decoherence-free subspace; all additional errors are corrected by a purification protocol. This approach may find application in quantum computation, communication, and metrology.
Alternative URL (local restricted copy) - V. Steixner, P. Rabl, P. Zoller, Quantum feedback cooling of a single trapped ion in front of a mirror, Phys. Rev. A 72, 043826, (2005), URL doi:10.1103/PhysRevA.72.043826 (ID: 308208) Toggle Abstract
We develop a theory of quantum feedback cooling of a single ion trapped in front of a mirror. By monitoring the motional sidebands of the light emitted into the mirror mode we infer the position of the ion, and act back with an appropriate force to cool the ion. We derive a feedback master equation along the lines of the quantum feedback theory developed by Wiseman and Milburn, which provides us with cooling times and final temperatures as a function of feedback gain and various system parameters.
Alternative URL (local restricted copy) - J. J. García-Ripoll, P. Zoller, J. I. Cirac, Coherent control of trapped ions using off-resonant lasers, Phys. Rev. A 71, 062309, (2005), URL doi:10.1103/PhysRevA.71.062309 (ID: 308224) Toggle Abstract
In this paper we develop a unified framework to study the coherent control of trapped ions subject to state-dependent forces. Taking different limits in our theory, we can reproduce previous designs of quantum gates and propose a different design of fast gates based on continuous laser beams. We demonstrate how to simulate Ising Hamiltonians in a many ions setup, and how to create highly entangled states and induce squeezing. Finally, in a detailed analysis we identify the physical limits of this technique and study the dependence of errors on the temperature.
Alternative URL (local restricted copy) - A. Recati, P. O. Fedichev, W. Zwerger, J. von Delft, P. Zoller, Atomic Quantum Dots Coupled to a Reservoir of a Superfluid Bose-Einstein Condensate, Phys. Rev. Lett. 94, 040404, (2005), URL doi:10.1103/PhysRevLett.94.040404 (ID: 308229) Toggle Abstract
We study the dynamics of an atomic quantum dot, i.e., a single atom in a tight optical trap which is coupled to a superfluid reservoir via laser transitions. Quantum interference between the collisional interactions and the laser induced coupling results in a tunable dot-bath coupling, allowing an essentially complete decoupling from the environment. Quantum dots embedded in a 1D Luttinger liquid of cold bosonic atoms realize a spin-boson model with Ohmic coupling, which exhibits a dissipative phase transition and allows us to directly measure atomic Luttinger parameters.
- H. Büchler, M. Hermele, S. D. Huber, M. P. Fisher, P. Zoller, Atomic quantum simulator for lattice gauge theories and ring exchange models, Phys. Rev. Lett. 95, 040402, (2005), oai:arXiv.org:cond-mat/0503254 (ID: 302730) Toggle Abstract
We present the design of a ring exchange interaction in cold atomic gases subjected to an optical lattice using well understood tools for manipulating and controlling such gases. The strength of this interaction can be tuned independently and describes the correlated hopping of two bosons. We discuss a setup where this coupling term may allows for the realization and observation of exotic quantum phases, including a deconfined insulator described by the Coulomb phase of a three-dimensional U(1) lattice gauge theory.
Alternative URL (local restricted copy) - L. Tian, R. Blatt, P. Zoller, Scalable ion trap quantum computing without moving ions, Eur. Phys. J. D 32, 201-208, (2005), URL doi:10.1140/epjd/e2004-00172-5 (ID: 308239) Toggle Abstract
A hybrid quantum computing scheme is studied where the hybrid qubit is made of an ion trap qubit serving as the information storage and a solid-state charge qubit serving as the quantum processor, connected by a superconducting cavity. In this paper, we extend our previous work [1] and study the decoherence, coupling and scalability of the hybrid system. We present our calculations of the decoherence of the coupled ion-charge system due to the charge fluctuations in the solid-state system and the dissipation of the superconducting cavity under laser radiation. A gate scheme that exploits rapid state flips of the charge qubit to reduce decoherence by the charge noise is designed. We also study a superconducting switch that is inserted between the cavity and the charge qubit and provides tunable coupling between the qubits. The scalability of the hybrid scheme is discussed together with several potential experimental obstacles in realizing this scheme.
- W. H. Zurek, U. Dorner, P. Zoller, Dynamics of a Quantum Phase Transition, Phys. Rev. Lett. 95, 105701, (2005-09-00), URL doi:10.1103/PhysRevLett.95.105701 (ID: 325892) Toggle Abstract
We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.
Alternative URL (local restricted copy) - P. Rabl, V. Steixner, P. Zoller, Quantum-limited velocity readout and quantum feedback cooling of a trapped ion via electromagnetically induced transparency, Phys. Rev. A 72, 043823, (2005), URL doi:10.1103/PhysRevA.72.043823 (ID: 308209) Toggle Abstract
We discuss continuous observation of the momentum of a single atom by employing the high velocity sensitivity of the index of refraction in a driven Lambda-system based on electromagnetically induced transparency. In the ideal limit of unit collection efficiency this provides a quantum-limited measurement with minimal backaction on the atomic motion. A feedback loop, which drives the atom with a force proportional to measured signal, provides a cooling mechanism for the atomic motion. We derive the master equation which describes the feedback cooling and show that in the Lamb-Dicke limit the steady state energies are close to the ground state, limited only by the photon collection efficiency. Outside of the Lamb-Dicke regime the predicted temperatures are well below the Doppler limit.
Alternative URL (local restricted copy) - J. I. Cirac, P. Zoller, Qubits, Gatter und Register, Physik Journal 11, 31, (2005-10-00), URL (ID: 332271)
- A. Micheli, P. Zoller, Protected Quantum Memory and Quantum Communication with polar hetero-nuclear molecules in two-dimensional Optical Lattices, 2nd Term-Review of the SFB (Innsbruck, Austria, 2005-01-00),
(2005), (ID: 332442)
- A. Micheli, P. Zoller, Protected Quantum Memory and Quantum Communication with polar hetero-nuclear molecules in two-dimensional Optical Lattices, Obergurgl Quantum Optics Meeting 2005 (Obergurgl, Austria, 2005-02-27), URL
(2005), (ID: 332444)
- V. Steixner, P. Rabl, P. Zoller, Feedback cooling of trapped ions, Obergurgl Quantum Optics Meeting 2005 URL
(2005-03-03), (ID: 326842)
- K. Jähne, P. Rabl, I. Wilson-Rae, P. Zoller, Cavity QED with superconducting qubits and quantum state transfer in such a system, Obergurgl Quantum Optics Meeting URL
(2005-03-00), (ID: 326857) Toggle Abstract
A Cooper pair box is a promising candidate for the realization of a qubit in a solid state environment. Recently, it has been demonstrated that such a qubit can be strongly coupled to the radiation field in a microwave cavity [1].
The system, consisting of a Cooper box that is located at the center of a transmission line, forms one node of a network, whilst different nodes are connected by other transmission lines. Motivated by the proposal of ref. [2], we want to investigate, whether ideal quantum state transfer can be achieved for this system.
[1] A. Wallraff, D. I. Schuster, A. Blais, L. Frunzio, R.-S. Huang, J. Majer, S.
Kumar, S. M. Girvin, and R. J. Schoelkopf, Nature 431, 162 (2004)
[2] J. I. Cirac, P. Zoller, H. J. Kimble, and H. Mabuchi, Phys. Rev. Lett. 78,
3221 (1996).
- A. J. Daley, A. Micheli, D. Jaksch, P. Zoller, The Single Atom Transistor, Exact Time Dependent Studies of 1D Systems, and Spectroscopy of Many Body Wavefunctions, Obergurgl Quantum Optics Meeting (Obergurgl, Austria, 2005-02-27),
(2005-02-27), (ID: 332783)
- K. Jähne, P. Rabl, I. Wilson-Rae, P. Zoller, Cavity QED with superconducting qubits and quantum state transfer in such a system, 11th Young Atom Opticians (YAO) Conference URL
(2005-02-00), (ID: 326872) Toggle Abstract
A Cooper pair box is a promising candidate for the realization of a qubit in a solid state environment. Recently, it has been demonstrated that such a qubit can be strongly coupled to the radiation field in a microwave cavity [1].
The system, consisting of a Cooper box that is located at the center of a transmission line, forms one node of a network, whilst different nodes are connected by other transmission lines. Motivated by the proposal of ref. [2], we want to investigate, whether ideal quantum state transfer can be achieved for this system.
[1] A. Wallraff, D. I. Schuster, A. Blais, L. Frunzio, R.-S. Huang, J. Majer, S.
Kumar, S. M. Girvin, and R. J. Schoelkopf, Nature 431, 162 (2004)
[2] J. I. Cirac, P. Zoller, H. J. Kimble, and H. Mabuchi, Phys. Rev. Lett. 78,
3221 (1996)
- S. Morrison, H. Büchler, A. J. Daley, H. Katzgraber, M. Lewenstein, P. Zoller, Replicas in Disordered Cold Atomic Gases, Quantum Optics Obergurgl meeting (Obergurgl, Austria, 2005-02-27),
(2005-02-27), (ID: 332791)
- S. Morrison, H. Büchler, A. J. Daley, H. Katzgraber, M. Lewenstein, P. Zoller, Replicas in Disordered Cold Atomic Gases, Theory of Cold Gases Conference, Cortona (Cortona, Italy, 2005-10-29),
(2005-10-29), (ID: 332790)
- H. Büchler, M. Hermele, S. D. Huber, M. P. Fisher, P. Zoller, Atomic Quantum Simulation of Lattice Gauge Theories and Ring Exchange, Bose-Einstein Condensation (San Feliu de Guixols, Spain, 2005-09-10), URL
(2005-09-10), (ID: 332062)
- A. J. Daley, A. Griessner, D. Jaksch, P. Zoller, Phonons as a new Element of the Optical Lattices Toolbox: Non-destructive Qubit Cooling and Register Initialisation, ESF-JSPS Frontier Science Conference Seies for Young Researchers: Quantum Information and Quantum Physics (Shonan Village Center, Japan, 2005-03-00),
(2005-03-00), (ID: 332782)
- P. O. Fedichev, M. J. Bijlsma, P. Zoller, Extended Molecules and Geometric Scattering Resonances in Optical Lattices, Phys. Rev. Lett. 92, 080401, (2004-02-00), URL doi:10.1103/PhysRevLett.92.080401 (ID: 324597) Toggle Abstract
We develop a theory describing neutral atom scattering at low energies in an optical lattice. We show that, for a repulsive interaction, as the microscopic scattering length increases the effective scattering amplitude approaches a limiting value which depends only on the lattice parameters. In the case of attractive interaction a geometric resonance occurs before reaching this limit. Close to the resonance, the effective interaction becomes repulsive and supports a weakly bound state, which can extend over several lattice sites.
- A. J. Daley, P. O. Fedichev, P. Zoller, Single-atom cooling by superfluid immersion: A nondestructive method for qubits, Phys. Rev. A 69, 022306, (2004-02-00), URL doi:10.1103/PhysRevA.69.022306 (ID: 324602) Toggle Abstract
We present a scheme to cool the motional state of neutral atoms confined in sites of an optical lattice by immersing the system in a superfluid. The motion of the atoms is damped by the generation of excitations in the superfluid, and under appropriate conditions the internal state of the atom remains unchanged. This scheme can thus be used to cool atoms used to encode a series of entangled qubits nondestructively. Within realizable parameter ranges, the rate of cooling to the ground state is found to be sufficiently large to be useful in experiments.
- T. Calarco, U. Dorner, P. S. Julienne, C. Williams, P. Zoller, Quantum computations with atoms in optical lattices: Marker qubits and molecular interactions, Phys. Rev. A 70, 012306, (2004), URL doi:10.1103/PhysRevA.70.012306 (ID: 314632) Toggle Abstract
We develop a scheme for quantum computation with neutral atoms, based on the concept of "marker" atoms, i.e., auxiliary atoms that can be efficiently transported in state-independent periodic external traps to operate quantum gates between physically distant qubits. This allows for relaxing a number of experimental constraints for quantum computation with neutral atoms in microscopic potential, including single-atom laser addressability. We discuss the advantages of this approach in a concrete physical scenario involving molecular interactions.
Alternative URL (local restricted copy) - J. I. Cirac, P. Zoller, New Frontiers in Quantum Information With Atoms and Ions,, Physics Today 38-44, (2004-03-00), URL (ID: 324583) Toggle Abstract
Both the precision control of trapped-ion systems and very large samples of cold neutral atoms are opening important new possibilities for quantum computation and simulation
Alternative URL (local restricted copy) - A. Micheli, A. J. Daley, D. Jaksch, P. Zoller, Single Atom Transistor in a 1D Optical Lattice, Phys. Rev. Lett. 93, 140408, (2004), URL doi:10.1103/PhysRevLett.93.140408 (ID: 314620) Toggle Abstract
We propose a scheme utilizing a quantum interference phenomenon to switch the transport of atoms in a 1D optical lattice through a site containing an impurity atom. The impurity represents a qubit which in one spin state is transparent to the probe atoms, but in the other acts as a single atom mirror. This allows a single-shot quantum nondemolition measurement of the qubit spin.
Alternative URL (local restricted copy) - E. Pazy, T. Calarco, P. Zoller, Spin state readout by quantum jump technique: for the purpose of quantum computing, IEEE Transactions on Nanotechnology 3, 10 - 16, (2004), URL doi:10.1109/TNANO.2003.820516 (ID: 314773) Toggle Abstract
Utilizing the Pauli-blocking mechanism we show that shining circular polarized light on a singly-charged quantum dot induces spin dependent fluorescence. Employing the quantum-jump technique we demonstrate that this resonance luminescence, due to a spin dependent optical excitation, serves as an excellent readout mechanism for measuring the spin state of a single electron confined to a quantum dot.
- B. Paredes, P. Zoller, J. I. Cirac, J. J. García-Ripoll, Strong correlation effects and quantum information theory of low dimensional atomic gases, J. Phys. IV 116, 135-168, (2004), URL DOI:10.1051/jp4:2004116005 (ID: 314540) Toggle Abstract
These lecture notes present an introduction to the strongly correlated regime of low dimensional atomic gases. The discussion is concentrated on situations in which the strongly correlated limit is achieved by creating degeneracies in the one-particle motional states. Three different schemes of experimental relevance are analyzed: bosonic atoms in a two dimensional rapidly rotating trap, bosonic atoms in a one dimensional optical lattice, and bosonic atoms with frozen motional degrees of freedom and two internal states. The corresponding entangled multiparticle states (Laughlin liquids, Mott phases, squeezed states), and the different strongly correlated phenomena that appear (fermionization, fractional statistics) are studied. Emphasis is given to the possibility of observing novel strongly correlated phenomena as well as to the possible implementations for quantum computation and quantum information.
- P. Zoller, L. Tian, Coupled Ion-Nanomechanical Systems, Phys. Rev. Lett. 93, 266403, (2004), URL doi:10.1103/PhysRevLett.93.266403 (ID: 314555) Toggle Abstract
We study ions in a nanotrap, where the electrodes are nanomechanical resonators. The ions play the role of a quantum optical system that acts as a probe and control, and allows entanglement with or between nanomechanical resonators.
Alternative URL (local restricted copy) - W. V. Liu, F. Wilczek, P. Zoller, Spin-dependent Hubbard model and a quantum phase transition in cold atoms, Phys. Rev. A 70, 033603, (2004), URL doi:10.1103/PhysRevA.70.033603 (ID: 314622) Toggle Abstract
We describe an experimental protocol for introducing spin-dependent lattice structure in a cold atomic Fermi gas using lasers. It can be used to realize Hubbard models whose hopping parameters depend on spin and whose interaction strength can be controlled with an external magnetic field. We suggest that exotic superfluidities will arise in this framework. An especially interesting possibility is a class of states that support coexisting superfluid and normal components, even at zero temperature. The quantity of normal component varies with external parameters. We discuss some aspects of the quantum phase transition that arises at the point where it vanishes.
- I. Martin, A. Shnirman, L. Tian, P. Zoller, Ground-state cooling of mechanical resonators, Phys. Rev. B 69, 125339, (2004), URL doi:10.1103/PhysRevB.69.125339 (ID: 314642) Toggle Abstract
We propose an application of a single Cooper pair box (Josephson qubit) for active cooling of nanomechanical resonators. Latest experiments with Josephson qubits demonstrated that long coherence time of the order of microsecond can be achieved in special symmetry points. Here we show that this level of coherence is sufficient to perform an analog of the well known in quantum optics "laser" cooling of a nanomechanical resonator capacitively coupled to the qubit. By applying an ac driving to the qubit or the resonator, resonators with frequency of order 100 MHz and quality factors higher than 103 can be efficiently cooled down to their ground state, while lower-frequency resonators can be cooled down to micro-Kelvin temperatures. We also consider an alternative setup where dc-voltage-induced Josephson oscillations play the role of the ac driving and show that cooling is possible in this case as well.
Alternative URL (local restricted copy) - P. Rabl, A. Shnirman, P. Zoller, Generation of Squeezed States of Nanomechanical Resonators by Reservoir Engineering, Phys. Rev. B 70, 205304, (2004), URL doi:10.1103/PhysRevB.70.205304 (ID: 335015) Toggle Abstract
An experimental demonstration of a nonclassical state of a nanomechanical resonator is still an outstanding task. In this paper we show how the resonator can be cooled and driven into a squeezed state by a bichromatic microwave coupling to a charge qubit. The stationary resonator state exhibits a reduced noise in one of the quadrature components by a factor of 0.5–0.2. These values are obtained for a 100 MHz resonator with a Q-value of 104 to 105 and for support temperatures of T[approximate]25 mK. We show that the coupling to the charge qubit can also be used to detect the squeezed state via measurements of the excited state population. Furthermore, by extending this measurement procedure a complete quantum state tomography of the resonator state can be performed. This provides a universal tool to detect a large variety of different states and to prove the quantum nature of nanomechanical systems.
Alternative URL (local restricted copy) - H. Büchler, P. Zoller, W. Zwerger, Spectroscopy of Superfluid Pairing in Atomic Fermi Gases, Phys. Rev. Lett. 93, 080401, (2004), URL doi:10.1103/PhysRevLett.93.080401 (ID: 314630) Toggle Abstract
We study the dynamic structure factor for density and spin within the crossover from BCS superfluidity of atomic fermions to the Bose-Einstein condensation of molecules. Both structure factors are experimentally accessible via Bragg spectroscopy and allow for the identification of the pairing mechanism: the spin structure factor allows for the determination of the two particle gap, while the collective sound mode in the density structure reveals the superfluid state.
Alternative URL (local restricted copy) - J. J. García-Ripoll, J. I. Cirac, P. Zoller, C. Kollath, U. Schollwöck, J. von Delft, Variational ansatz for the superfluid Mott-insulator transition in optical lattices, Opt. Express 12, 42-54, (2004), URL oai:arXiv.org:cond-mat/0306162 (ID: 314640) Toggle Abstract
We develop a variational wave function for the ground state of a one-dimensional bosonic lattice gas. The variational theory is initially developed for the quantum rotor model and later on extended to the Bose- Hubbard model. This theory is compared with quasi-exact numerical results obtained by Density Matrix Renormalization Group (DMRG) studies and with results from other analytical approximations. Our approach accurately gives local properties for strong and weak interactions, and it also describes the crossover from the superfluid phase to the Mott-insulator phase.
- A. Griessner, D. Jaksch, P. Zoller, Cavity-assisted nondestructive laser cooling of atomic qubits, J. Phys. B: At. Mol. Opt. Phys. 37, 1419, (2004), URL doi:10.1088/0953-4075/37/7/004 (ID: 335134) Toggle Abstract
We analyse two configurations for laser cooling of neutral atoms whose internal states store qubits. The atoms are trapped in an optical lattice which is placed inside a cavity. We show that the coupling of the atoms to the damped cavity mode can provide a mechanism which leads to cooling of the motion without destroying the quantum information.
Alternative URL (local restricted copy) - I. Wilson-Rae, P. Zoller, A. Imamoglu, Laser Cooling of a Nanomechanical Resonator Mode to its Quantum Ground State, Phys. Rev. Lett. 92, 075507, (2004), URL doi:10.1103/PhysRevLett.92.075507 (ID: 336649) Toggle Abstract
We show that it is possible to cool a nanomechanical resonator mode to its ground state. The proposed technique is based on resonant laser excitation of a phonon sideband of an embedded quantum dot. The strength of the sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot optical transition. Possible applications of this scheme include generation of nonclassical states of mechanical motion.
- L. Tian, P. Rabl, R. Blatt, P. Zoller, Interfacing Quantum-Optical and Solid-State Qubits, Phys. Rev. Lett. 92, 247902, (2004), URL doi:10.1103/PhysRevLett.92.247902 (ID: 314633) Toggle Abstract
We present a generic model of coupling quantum-optical and solid-state qubits, and the corresponding transfer protocols. The example discussed is a trapped ion coupled to a charge qubit (e.g., Cooper pair box). To enhance the coupling and to achieve compatibility between the different experimental setups we introduce a superconducting cavity as the connecting element.
- L. Jacak, P. Machnikowski, J. Krasnyj, P. Zoller, Coherent and incoherent phonon processes in artificial atoms Optical Physics, The European Physical Journal D 22 / 3, 319 - 331, (2003-05-00), URL doi:10.1140/epjd/e2003-00020-2 (ID: 375605) Toggle Abstract
Carrier-phonon interaction in semiconductor quantum dots leads to three classes of phenomena: coherent effects (spectrum reconstruction) due to the nearly-dispersionless LO phonons, incoherent effects (transitions) induced by acoustical phonons and dressing phenomena, related to non-adiabatic, sub-picosecond excitation. Polaron spectra, relaxation times and dressing-related decoherence rates are calculated, in accordance with experiment.
- E. Pazy, T. Calarco, I. D'Amico, P. Zanardi, F. Rossi, P. Zoller, All Optical Spin-Based Quantum Information Processing, Journal of Superconductivity 16/2, 383 - 385, (2003-04-01), URL doi:10.1023/A:1023646326888 (ID: 375698) Toggle Abstract
We propose a spin-based ultra-fast laser driven implementation of quantum information processing based on the Pauli blocking effect in semiconductors, which acts as a spin dependent switching mechanism for auxiliary exciton states.
spintronics - quantum information - quantum dot - Pauli blocking effect
- B. Damski, J. Zakrzewski, L. Santos, P. Zoller, M. Lewenstein, Atomic Bose and Anderson Glasses in Optical Lattices, Phys. Rev. Lett. 91, 080403, (2003), URL doi:10.1103/PhysRevLett.91.080403 (ID: 336658) Toggle Abstract
An ultracold atomic Bose gas in an optical lattice is shown to provide an ideal system for the controlled analysis of disordered Bose lattice gases. This goal may be easily achieved under the current experimental conditions by introducing a pseudorandom potential created by a second additional lattice or, alternatively, by placing a speckle pattern on the main lattice. We show that, for a noncommensurable filling factor, in the strong-interaction limit, a controlled growing of the disorder drives a dynamical transition from superfluid to Bose-glass phase. Similarly, in the weak interaction limit, a dynamical transition from superfluid to Anderson-glass phase may be observed. In both regimes, we show that even very low-intensity disorder-inducing lasers cause large modifications of the superfluid fraction of the system.
- J. I. Cirac, P. Zoller, How to Manipulate Cold Atoms, Science 301, 176, (2003), URL doi:10.1126/science.1085130 (ID: 336660) Toggle Abstract
Since Bose-Einstein condensates were first realized in 1995, experimentalists have focused on characterizing and manipulating these weakly interacting systems. In their Perspective, Cirac and Zoller look ahead toward the next challenge for atomic physics: strongly interacting atomic systems that may be of use in quantum computing and may clarify fundamental properties of quantum mechanics. They explain how optical lattices can be used to tune the interactions between cold atoms and how a quantum simulator may be constructed. The latter may enable the first quantum computers that can outperform ordinary computers for nontrivial problems.
- E. Pazy, T. Calarco, I. D'Amico, P. Zanardi, F. Rossi, P. Zoller, Implementation of an all-optical spin-based quantum computer, Physica Status Solidi B 238, 411, (2003), URL doi:10.1002/pssb.200303154 (ID: 336659) Toggle Abstract
An all-optical implementation scheme of a spin-based quantum computer is presented. Our quantum memory consists of the spin of electrons confined to quantum dots. Utilizing the Pauli blocking effect we are able to have ultra-fast control and read out of the electronic spin degrees of freedom by conditionally coupling them with charged excitations of the quantum dot. Imperfections effecting gate operations are discussed and we show that final readout can still be performed by a quantum-jump technique even in the presence of hole mixing, when the Pauli-blocking selection rule is violated.
- D. Jaksch, P. Zoller, Creation of effective magnetic fields in optical lattices: the Hofstadter butterfly for cold neutral atoms, New Journal of Physics 5, 56, (2003), URL doi:10.1088/1367-2630/5/1/356 (ID: 336661) Toggle Abstract
We investigate the dynamics of neutral atoms in a 2D optical lattice which traps two distinct internal states of the atoms in different columns. Two Raman lasers are used to coherently transfer atoms from one internal state to the other, thereby causing hopping between the different columns. By adjusting the laser parameters appropriately we can induce a non-vanishing phase of particles moving along a closed path on the lattice. This phase is proportional to the enclosed area and we thus simulate a magnetic flux through the lattice. This set-up is described by a Hamiltonian identical to the one for electrons on a lattice subject to a magnetic field and thus allows us to study this equivalent situation under very well defined controllable conditions. We consider the limiting case of huge magnetic fields—which is not experimentally accessible for electrons in metals—where a fractal band structure, the Hofstadter butterfly, characterizes the system.
- E. Jané, G. Vidal, W. Dür, P. Zoller, J. I. Cirac, Simulation of quantum dynamics with quantum optical systems, Quantum Information and Computation (online) 3, 15, (2003), URL (ID: 336662) Toggle Abstract
We propose the use of quantum optical systems to perform universal simulation of quantum dynamics. Two specific implementations that require present technology are put forward for illustrative purposes. The first scheme consists of neutral atoms stored in optical lattices, while the second scheme consists of ions stored in an array of micro--traps. Each atom (ion) supports a two--level system, on which local unitary operations can be performed through a laser beam. A raw interaction between neighboring two--level systems is achieved by conditionally displacing the corresponding atoms (ions) Then, average Hamiltonian techniques are used to achieve evolutions in time according to a large class of Hamiltonians.
- E. Pazy, E. Biolatti, T. Calarco, I. D'Amico, P. Zanardi, F. Rossi, P. Zoller, Spin-based optical quantum computation via Pauli blocking in semiconductor quantum dots, Europhys. Lett. 62, 175, (2003), URL doi:10.1209/epl/i2003-00343-4 (ID: 336663) Toggle Abstract
We present a solid-state implementation of an all-optical spin-based quantum computer. Our proposal for a quantum-computing device is based on the spin degrees of freedom of electrons confined in semiconductor quantum dots, thus benefitting from relatively long coherence times. Combining Pauli blocking effects with properly tailored ultrafast laser pulses, we obtain sub-picosecond spin-dependent switching of the Coulomb interaction, which is the essence of our gating operations. This allows us to realize fast quantum gates which do not translate into fast decoherence times and pave the way for an all-optical spin-based quantum computer.
- A. Recati, P. O. Fedichev, W. Zwerger, P. Zoller, Spin-Charge Separation in Ultracold Quantum Gases, Phys. Rev. Lett. 90, 020401, (2003), URL doi:10.1103/PhysRevLett.90.020401 (ID: 336665) Toggle Abstract
We investigate the physical properties of quasi-1D quantum gases of fermionic atoms confined in harmonic traps. Using the fact that for a homogeneous gas the low-energy properties are exactly described by a Luttinger model, we analyze the nature and manifestations of spin-charge separation, where in the case of atoms "spin" and "charge" refer to two internal atomic states and the atomic mass density, respectively. We discuss the necessary physical conditions and experimental limitations confronting possible experimental implementations.
- A. Micheli, D. Jaksch, J. I. Cirac, P. Zoller, Many-particle entanglement in two-component Bose-Einstein condensates, Phys. Rev. A 67, 013607, (2003), URL doi:10.1103/PhysRevA.67.013607 (ID: 336666) Toggle Abstract
We investigate schemes to dynamically create many-particle entangled states of a two-component Bose-Einstein condensate in a very short time proportional to 1/N, where N is the number of condensate particles. For small N we compare exact numerical calculations with analytical semiclassical estimates and find very good agreement for N>=50. We also estimate the effect of decoherence on our scheme, study possible scenarios for measuring the entangled states, and investigate experimental imperfections.
- B. Damski, L. Santos, E. Tiemann, M. Lewenstein, S. Kotochigova, P. S. Julienne, P. Zoller, Creation of a Dipolar Superfluid in Optical Lattices, Phys. Rev. Lett. 90, 110401, (2003), URL doi:10.1103/PhysRevLett.90.110401 (ID: 336664) Toggle Abstract
We show that, by loading a Bose-Einstein condensate of two different atomic species into an optical lattice, it is possible to achieve a Mott-insulator phase with exactly one atom of each species per lattice site. A subsequent photoassociation leads to the formation of one heteronuclear molecule with a large electric dipole moment, at each lattice site. The melting of such a dipolar Mott insulator creates a dipolar superfluid, and eventually a dipolar molecular condensate.
- T. Calarco, A. Datta, P. O. Fedichev, E. Pazy, P. Zoller, Spin-based all-optical quantum computation with quantum dots: Understanding and suppressing decoherence, Phys. Rev. A 68, 012310, (2003), URL doi:10.1103/PhysRevA.68.012310 (ID: 336655) Toggle Abstract
We present an all-optical implementation of quantum computation using semiconductor quantum dots. Quantum memory is represented by the spin of an excess electron stored in each dot. Two-qubit gates are realized by switching on trion-trion interactions between different dots. State selectivity is achieved via conditional laser excitation exploiting Pauli exclusion principle. Read out is performed via a quantum-jump technique. We analyze the effect on our scheme's performance of the main imperfections present in real quantum dots: exciton decay, hole mixing, and phonon decoherence. We introduce an adiabatic gate procedure that allows one to circumvent these effects and evaluate quantitatively its fidelity.
- U. Dorner, P. O. Fedichev, D. Jaksch, M. Lewenstein, P. Zoller, Entangling Strings of Neutral Atoms in 1D Atomic Pipeline Structures, Phys. Rev. Lett. 91, 073601, (2003), URL doi:10.1103/PhysRevLett.91.073601 (ID: 336657) Toggle Abstract
We study a string of neutral atoms with nearest neighbor interaction in a 1D beam splitter configuration, where the longitudinal motion is controlled by a moving optical lattice potential. The dynamics of the atoms crossing the beam splitter maps to a 1D spin model with controllable time dependent parameters, which allows the creation of maximally entangled states of atoms by crossing a quantum phase transition. Furthermore, we show that this system realizes protected quantum memory, and we discuss the implementation of one- and two-qubit gates in this setup.
- P. Rabl, A. J. Daley, P. O. Fedichev, J. I. Cirac, P. Zoller, Defect-Suppressed Atomic Crystals in an Optical Lattice, Physical Review Letters 91, 110403, (2003), URL doi:10.1103/PhysRevLett.91.110403 (ID: 335014) Toggle Abstract
We present a coherent filtering scheme which dramatically reduces the site occupation number defects for atoms in an optical lattice by transferring a chosen number of atoms to a different internal state via adiabatic passage. With the addition of superlattices it is possible to engineer states with a specific number of atoms per site (atomic crystals), which are required for quantum computation and the realization of models from condensed matter physics, including doping and spatial patterns. The same techniques can be used to measure two-body spatial correlation functions.
- J. I. Cirac, L. Duan, D. Jaksch, P. Zoller, Quantum information processing with quantum optics, Ann. Henri Poincare 4, 661, (2003), (ID: 336650) Toggle Abstract
We review theoretical proposals for implementation of quantum computing and quantum communication with quantum optical methods.
- A. Imamoglu, E. Knill, L. Tian, P. Zoller, Optical Pumping of Quantum-Dot Nuclear Spins, Phys. Rev. Lett. 91, 017402, (2003), URL doi:10.1103/PhysRevLett.90.017402 (ID: 336656) Toggle Abstract
Hyperfine interactions with randomly oriented nuclear spins present a fundamental decoherence mechanism for electron spin in a quantum dot, that can be suppressed by polarizing the nuclear spins. Here, we analyze an all-optical scheme that uses hyperfine interactions to implement laser cooling of quantum-dot nuclear spins. The limitation imposed on spin cooling by the dark states for collective spin relaxation can be overcome by modulating the electron wave function.
- L. Tian, P. Zoller, Quantum computing with atomic Josephson junction arrays, Phys. Rev. A 68, 042321, (2003), URL doi:10.1103/PhysRevA.68.042321 (ID: 336652) Toggle Abstract
We present a quantum computing scheme with atomic Josephson junction arrays. The system consists of a small number of atoms with three internal states and trapped in a far-off-resonant optical lattice. Raman lasers provide the "Josephson" tunneling, and the collision interaction between atoms represent the "capacitive" couplings between the modes. The qubit states are collective states of the atoms with opposite persistent currents. This system is closely analogous to the superconducting flux qubit. Single-qubit quantum logic gates are performed by modulating the Raman couplings, while two-qubit gates result from a tunnel coupling between neighboring wells. Readout is achieved by tuning the Raman coupling adiabatically between the Josephson regime to the Rabi regime, followed by a detection of atoms in internal electronic states. Decoherence mechanisms are studied in detail promising a high ratio between the decoherence time and the gate operation time.
- A. Recati, P. O. Fedichev, W. Zwerger, P. Zoller, Fermi 1D quantum gas: Luttinger liquid approach and spin-charge separation, J. Opt. B: Quantum Semiclass. Opt. 5, 55, (2003), URL doi:10.1088/1464-4266/5/2/359 (ID: 336651) Toggle Abstract
We discuss the properties of quasi-1D quantum gases of fermionic atoms using the Luttinger liquid theory, including the presence of an optical lattice and of a longitudinal trapping potential. We analyze in particular the nature and manifestations of spin-charge separation, where in the case of atoms ``spin'' and ``charge'' refers to two internal atomic states and the atomic mass density, respectively.
- J. J. García-Ripoll, P. Zoller, J. I. Cirac, Speed Optimized Two-Qubit Gates with Laser Coherent Control Techniques for Ion Trap Quantum Computing, Phys. Rev. Lett. 91, 157901, (2003), URL doi:10.1103/PhysRevLett.91.157901 (ID: 336653) Toggle Abstract
We propose a new concept for a two-qubit gate operating on a pair of trapped ions based on laser coherent control techniques. The gate is insensitive to the temperature of the ions, works also outside the Lamb-Dicke regime, requires no individual addressing by lasers, and can be orders of magnitude faster than the trap period, which is presently the speed limit of all two-qubit proposals.
- D. Jaksch, V. Venturi, J. I. Cirac, C. Williams, P. Zoller, Creation of a Molecular Condensate by Dynamically Melting a Mott Insulator, Phys. Rev. Lett. 89, 040402, (2002-07-02), URL doi:10.1103/PhysRevLett.89.040402 (ID: 337573) Toggle Abstract
We propose the creation of a molecular Bose-Einstein condensate by loading an atomic condensate into an optical lattice and driving it into a Mott insulator with exactly two atoms per site. Molecules in a Mott insulator state are then created under well defined conditions by photoassociation with essentially unit efficiency. Finally, the Mott insulator is melted and a superfluid state of the molecules is created. We study the dynamics of this process and photoassociation of tightly trapped atoms.
- L. Duan, J. I. Cirac, P. Zoller, Three-dimensional theory for interaction between atomic ensembles and free-space light, Phys. Rev. A 66, 023818, (2002-08-27), URL doi:10.1103/PhysRevA.66.023818 (ID: 337569) Toggle Abstract
Atomic ensembles have shown to be a promising candidate for implementations of quantum information processing by many recently discovered schemes. All these schemes are based on the interaction between optical beams and atomic ensembles. For description of these interactions, one assumed either a cavity-QED model or a one-dimensional light propagation model, which is still inadequate for a full prediction and understanding of most of the current experimental efforts that are actually taken in the three-dimensional free space. Here, we propose a perturbative theory to describe the three-dimensional effects in interaction between atomic ensembles and free-space light with a level configuration important for several applications. The calculations reveal some significant effects that were not known before from the other approaches, such as the inherent mode-mismatching noise and the optimal mode-matching conditions. The three-dimensional theory confirms the collective enhancement of the signal-to-noise ratio which is believed to be one of the main advantages of the ensemble-based quantum information processing schemes, however, it also shows that this enhancement needs to be understood in a more subtle way with an appropriate mode-matching method.
- A. Recati, T. Calarco, P. Zanardi, J. I. Cirac, P. Zoller, Holonomic quantum computation with neutral atoms, Phys. Rev. A 66, 032309, (2002-09-17), URL doi:10.1103/PhysRevA.66.032309 (ID: 337570) Toggle Abstract
We propose an all-geometric implementation of quantum computation using neutral atoms in cavity QED. We show how to perform generic single- and two-qubit gates, the latter by encoding a two-atom state onto a single, many-level atom. We compare different strategies to overcome limitations due to cavity imperfections.
- W. Hofstetter, J. I. Cirac, P. Zoller, E. Demler, M. Lukin, High-Temperature Superfluidity of Fermionic Atoms in Optical Lattices, Phys. Rev. Lett. 89, 220407, (2002-11-12), URL doi:10.1103/PhysRevLett.89.220407 (ID: 337567) Toggle Abstract
Fermionic atoms confined in a potential created by standing wave light can undergo a phase transition to a superfluid state at a dramatically increased transition temperature. Depending upon carefully controlled parameters, a transition to a superfluid state of Cooper pairs, antiferromagnetic states or d-wave pairing states can be induced and probed under realistic experimental conditions. We describe an atomic physics experiment that can provide critical insight into the origin of high-temperature superconductivity in cuprates.
- B. Paredes, P. Zoller, J. I. Cirac, Fermionizing a small gas of ultracold bosons, Phys. Rev. A 66, 033609, (2002-09-20), URL doi:10.1103/PhysRevA.66.033609 (ID: 337568) Toggle Abstract
We study the physics of a rapidly rotating gas of ultracold atomic bosons, with an internal degree of freedom. We show that in the limit of rapid rotation of the trap the problem exactly maps onto that of noninteracting fermions with spin in the lowest Landau level. The spectrum of the real bosonic system is identical to the one of the effective fermions, with the same eigenvalues and the same density of states. When the ratio of the number of atoms to the spin degeneracy is an integer number, the ground state for the effective fermions is an integer quantum Hall state. The corresponding bosonic state is a fractional quantum Hall liquid whose filling factor ranges in the sequence $\nu$= 1/2,2/3,3/4,..., as the spin degeneracy increases. Anyons with 1/2,1/3,1/4,... statistics can be created by inserting lasers with the appropriate polarizations. A special situation appears when the spin degeneracy equals the number of atoms in the gas. The ground state is then the product of a completely antisymmetric spin state and a nu= 1 Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics although the real components are bosonic atoms.
- U. Dorner, P. Zoller, Laser-driven atoms in half-cavities, Phys. Rev. A 66, 023816, (2002-08-26), URL doi:10.1103/PhysRevA.66.023816 (ID: 337571) Toggle Abstract
The behavior of a two-level atom in a half-cavity, i.e., a cavity with one mirror, is studied within the framework of a one-dimensional model with respect to spontaneous decay and resonance fluorescence. The system under consideration corresponds to the setup of a recently performed experiment [J. Eschner et al., Nature (London) 413, 495 (2001)] where the influence of a mirror on a fluorescing single atom was revealed. In the present work special attention is paid to the regime of large atom-mirror distances where intrinsic memory effects can not longer be neglected. This is done with the help of delay-differential equations which contain, for small atom-mirror distances, the Markovian limit with effective level shifts and decay rates leading to the phenomenon of enhancement or inhibition of spontaneous decay. Several features are recovered beyond an effective Markovian treatment, appearing in experimentally accessible quantities like the intensity or emission spectra of the scattered light.
- D. Jaksch, J. I. Cirac, P. Zoller, Dynamically turning off interactions in a two-component condensate, Phys. Rev. A 65, 033625, (2002-03-01), URL doi:10.1103/PhysRevA.65.033625 (ID: 337576) Toggle Abstract
We propose a mechanism to change the interaction strengths of a two-component condensate. It is shown that the application of pi/2 pulses allows us to alter the effective interspecies-interaction strength as well as the effective interaction strength between particles of the same kind. This mechanism provides a simple method to transform spatially stable condensates into unstable ones and vice versa. It also provides a means to store a squeezed spin state by turning off the interaction for the internal states and thus allows to gain control over many-body entangled states.
- L. Duan, J. I. Cirac, P. Zoller, Quantum entanglement in spinor Bose-Einstein condensates, Phys. Rev. A 65, 033619, (2002-02-27), URL doi:10.1103/PhysRevA.65.033619 (ID: 337577) Toggle Abstract
We propose a scheme to generate and detect various kinds of quantum entanglement in a spin-1 Bose-Einstein condensate. It is shown that substantial many-particle entanglement can be generated directly in the spin-1 condensate by free dynamical evolution with a properly prepared initial state. The scheme also provides a simple method to generate three-mode entanglement in the second-quantization picture and to detect the continuous variable type of entanglement between two effective modes in the spin-1 condensate.
- P. Zoller, Making it with molecules, Nature 417, 493, (2002-05-30), URL doi: 10.1038/417493a (ID: 337575) Toggle Abstract
Following the creation of atomic Bose–Einstein condensates in the mid-1990s, a major goal has been to produce a condensate of molecules.Technical challenges remain, but that achievement is now tantalizingly close.
- T. Calarco, D. Jaksch, J. I. Cirac, P. Zoller, Controlling dynamical phases in quantum optics,, J. Opt. B: Quantum Semiclass. Opt. 4, S430, (2002-07-29), URL doi:10.1088/1464-4266/4/4/334 (ID: 337572) Toggle Abstract
We review and compare several schemes for inducing precisely controlled quantum phases in quantum optical systems. We focus in particular onto conditional dynamical phases, i.e., phases obtained via state- and time-dependent interactions between trapped two-level atoms and ions. We describe different possibilities for the kind of interaction to be exploited, including cold controlled collisions, electrostatic forces, and dipole-dipole interactions.
- M. Lukin, M. Fleischhauer, R. Cote, L. Duan, D. Jaksch, J. I. Cirac, P. Zoller, Dipole Blockade and Quantum Information Processing in Mesoscopic Atomic Ensembles, Phys. Rev. Lett. 87, 037901, (2001-06-26), URL doi:10.1103/PhysRevLett.87.037901 (ID: 337584) Toggle Abstract
We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting "dipole blockade" can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.
- A. Sorensen, L. Duan, J. I. Cirac, P. Zoller, Many-particle entanglement with Bose−Einstein condensates, Nature 409, 63, (2001-01-04), URL doi:10.1038/35051038 (ID: 337588) Toggle Abstract
The possibility of creating and manipulating entangled states of systems of many particles is of significant interest for quantum information processing; such a capability could lead to new applications that rely on the basic principles of quantum mechanics1. So far, up to four atoms have been entangled in a controlled way. A crucial requirement for the production of entangled states is that they can be considered pure at the single-particle level. Bose−Einstein condensates fulfil this requirement; hence it is natural to investigate whether they can also be used in some applications of quantum information. Here we propose a method to achieve substantial entanglement of a large number of atoms in a Bose−Einstein condensate. A single resonant laser pulse is applied to all the atoms in the condensate, which is then allowed to evolve freely; in this latter stage, collisional interactions produce entanglement between the atoms. The technique should be realizable with present technology.
- C. Menotti, J. R. Anglin, J. I. Cirac, P. Zoller, Dynamic splitting of a Bose-Einstein condensate, Phys. Rev. A 63, 023601, (2001-01-04), URL doi:10.1103/PhysRevA.63.023601 (ID: 337590) Toggle Abstract
We study the dynamic process of splitting a condensate by raising a potential barrier in the center of a harmonic trap. We use a two-mode model to describe the phase coherence between the two halves of the condensate. Furthermore, we explicitly consider the spatial dependence of the mode funtions, which varies depending on the potential barrier. This allows us to get the tunneling coupling between the two wells and the on-site energy as a function of the barrier height. Moreover, we can get some insight into the collective modes that are excited by raising the barrier. We describe the internal and external degrees of freedom by variational ansatz. We distinguish the possible regimes as a function of the characteristic parameters of the problem and identify the adiabaticity conditions.
- T. Calarco, J. I. Cirac, P. Zoller, Entangling ions in arrays of microscopic traps, Phys. Rev. A 63, 062304, (2001-05-14), URL doi:10.1103/PhysRevA.63.062304 (ID: 337587) Toggle Abstract
We consider a system of particles in an array of microscopic traps, coupled to each other via electrostatic interaction, and pushed by an external state-dependent force. We show how to implement a two-qubit quantum gate between two such particles with a high fidelity.
- B. Paredes, P. O. Fedichev, J. I. Cirac, P. Zoller, (1/2)-Anyons in Small Atomic Bose-Einstein Condensates, Phys. Rev. Lett. 87, 010402, (2001-07-02), URL doi:10.1103/PhysRevLett.87.010402 (ID: 337583) Toggle Abstract
We discuss a way of creating, manipulating, and detecting anyons in rotating Bose-Einstein condensates consisting of a small number of atoms. By achieving a quasidegeneracy in the atomic motional states we drive the system into a (1/2)-Laughlin state for fractional quantum Hall bosons. Localized (1/2)-quasiholes can be created by focusing lasers at the desired positions. We show how to manipulate these quasiholes in order to probe directly their (1/2)-statistics.
- S. Gardiner, K. M. Gheri, P. Zoller, Cavity-assisted quasiparticle damping in a Bose-Einstein condensate, Phys. Rev. A 63, 051603(R), (2001-04-19), URL doi:10.1103/PhysRevA.63.051603 (ID: 337585) Toggle Abstract
We consider an atomic Bose-Einstein condensate held within an optical cavity and interacting with laser fields. We show how the interaction of the cavity mode with the condensate can cause energy due to excitations to be coupled to a lossy cavity mode, which then decays, thus damping the condensate. We show how to choose parameters for damping specific excitations, and how to target a range of different excitations to potentially produce extremely cold condensates.
- G. M. Bruun, P. Törmä, M. Rodriguez, P. Zoller, Laser probing of Cooper-paired trapped atoms, Phys. Rev. A 64, 033609, (2001-08-16), URL doi:10.1103/PhysRevA.64.033609 (ID: 337586) Toggle Abstract
We consider a gas of trapped Cooper-paired fermionic atoms that are manipulated by laser light. The laser induces a transition from an internal state with large negative scattering length (superfluid) to one with weaker interactions (normal gas). We show that the process can be used to detect the presence of the superconducting order parameter. Also, we propose a direct way of measuring the size of the gap in the trap. The efficiency and feasibility of this probing method is investigated in detail in different physical situations.
- L. J. Garay, J. R. Anglin, J. I. Cirac, P. Zoller, Sonic black holes in dilute Bose-Einstein condensates, Phys. Rev. A 63, 023611, (2001-01-17), URL doi:10.1103/PhysRevA.63.023611 (ID: 337591) Toggle Abstract
The sonic analog of a gravitational black hole in dilute-gas Bose-Einstein condensates is investigated. It is shown that there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit behaviors completely analogous to that of gravitational black holes. The dynamical instabilities involve the creation of quasiparticle pairs in positive and negative energy states. We illustrate these features in two qualitatively different one-dimensional models, namely, a long, thin condensate with an outcoupler laser beam providing an "atom sink," and a tight ring-shaped condensate. We also simulate the creation of a stable sonic black hole by solving the Gross-Pitaevskii equation numerically for a condensate subject to a trapping potential which is adiabatically deformed. A sonic black hole could, in this way, be created experimentally with state-of-the-art or planned technology.
- L. Duan, J. I. Cirac, P. Zoller, Geometric Manipulation of Trapped Ions for Quantum Computation, Science 292, 1695, (2001-06-01), URL doi:10.1126/science.1058835 (ID: 337578) Toggle Abstract
We propose an experimentally feasible scheme to achieve quantum computation based solely on geometric manipulations of a quantum system. The desired geometric operations are obtained by driving the quantum system to undergo appropriate adiabatic cyclic evolutions. Our implementation of the all-geometric quantum computation is based on laser manipulation of a set of trapped ions. An all-geometric approach, apart from its fundamental interest, offers a possible method for robust quantum computation.
- G. Giedke, L. Duan, J. I. Cirac, P. Zoller, Distillability Criterion for all bipartite Gaussian States, Quantum Information and Computation (online) 1, 79, (2001-10-00), URL (ID: 337581) Toggle Abstract
We prove that all inseparable Gaussian states of two modes can be distilled into maximally entangled pure states by local operations. Using this result we show that a bipartite Gaussian state of arbitrarily many modes can be distilled if and only if its partial transpose is not positive.
- D. Jaksch, S. Gardiner, K. Schulze, J. I. Cirac, P. Zoller, Uniting Bose-Einstein Condensates in Optical Resonators, Phys. Rev. Lett. 86, 004733, (2001-05-21), URL doi:10.1103/PhysRevLett.86.4733 (ID: 337582) Toggle Abstract
The relative phase of two initially independent Bose-Einstein condensates can be laser cooled to unite the two condensates by putting them into a ring cavity and coupling them with an internal Josephson junction. First, we show that this phase cooling process already appears within a semiclassical model. We calculate the stationary states, find regions of bistable behavior, and suggest a Ramsey-type experiment to measure the buildup of phase coherence between the condensates. We also study quantum effects and imperfections of the system.
- L. Duan, M. Lukin, J. I. Cirac, P. Zoller, Long-distance quantum communication with atomic ensembles and linear optics, Nature 414, 413, (2001-11-22), URL doi:10.1038/35106500 (ID: 337580) Toggle Abstract
Quantum communication holds promise for absolutely secure transmission of secret messages and the faithful transfer of unknown quantum states. Photonic channels appear to be very attractive for the physical implementation of quantum communication. However, owing to losses and decoherence in the channel, the communication fidelity decreases exponentially with the channel length. Here we describe a scheme that allows the implementation of robust quantum communication over long lossy channels. The scheme involves laser manipulation of atomic ensembles, beam splitters, and single-photon detectors with moderate efficiencies, and is therefore compatible with current experimental technology. We show that the communication efficiency scales polynomially with the channel length, and hence the scheme should be operable over very long distances.
- G. Giedke, B. Kraus, L. Duan, P. Zoller, M. Lewenstein, J. I. Cirac, Separability and Distillability of bipartite Gaussian States - the Complete Story, Fortschr. Phys. 49, 973, (2001-10-25), URL doi:10.1002/1521-3978(200110)49:10/11<973::AID-PROP973>3.0.CO;2-B (ID: 337579) Toggle Abstract
We present necessary and sufficient conditions for both the separability and the distillability of bipartite Gaussian states of an arbitrary number of modes. The conditions can be easily checked by direct calculations, thus providing operational criteria for both properties. This solves the separability and distillability problems for Gaussian states.
- J. J. García-Ripoll, J. I. Cirac, J. R. Anglin, V. M. Perez-Garcia, P. Zoller, Spin monopoles with Bose-Einstein condensates, Phys. Rev. A 61, 053609, (2000-04-17), URL doi:10.1103/PhysRevA.61.053609 (ID: 337609) Toggle Abstract
We study the feasibility of preparing a Bose-Einstein condensed sample of atoms in a macroscopic quantum state that resembles a spin monopole. In this state, the atomic internal spins lie in the x-y plane and point along the radial direction. The stability and dynamics of this structure are studied analytically in some cases and numerically in the more general situation. We find these structures to be stable objects giving rise to a nontrivial state of a Bose-Einstein condensate.
- P. Törmä, P. Zoller, Laser Probing of Atomic Cooper Pairs, Phys. Rev. Lett. 85, 487, (2000-07-17), URL doi:10.1103/PhysRevLett.85.487 (ID: 337603) Toggle Abstract
We consider a gas of attractively interacting cold fermionic atoms which are manipulated by laser light. The laser induces a transition from an internal state with large negative scattering length to one with almost no interactions. The process can be viewed as a tunneling of atomic population between the superconducting and the normal states of the gas. It can be used to detect the BCS ground state and to measure the superconducting order parameter.
- S. Gardiner, D. Jaksch, R. Dumhart, J. I. Cirac, P. Zoller, Nonlinear matter wave dynamics with a chaotic potential, Phys. Rev. A 62, 023612, (2000-07-20), URL doi:10.1103/PhysRevA.62.023612 (ID: 337604) Toggle Abstract
We consider the case of a cubic nonlinear Schrödinger equation with an additional chaotic potential, in the sense that such a potential produces chaotic dynamics in classical mechanics. We derive and describe an appropriate semiclassical limit to such a nonlinear Schrödinger equation, using a semiclassical interpretation of the Wigner function, and relate this to the hydrodynamic limit of the Gross-Pitaevskii equation used in the context of Bose-Einstein condensation. We investigate a specific example of a Gross-Pitaevskii equation with such a chaotic potential, the one-dimensional delta-kicked harmonic oscillator, and its semiclassical limit, discovering in the process an interesting interference effect, where increasing the strength of the repulsive nonlinearity promotes localization of the wave function. We explore the feasibility of an experimental realization of such a system in a Bose-Einstein condensate experiment, giving a concrete proposal of how to implement such a configuration, and considering the problem of condensate depletion.
- C. Saavedra, K. M. Gheri, P. Törmä, J. I. Cirac, P. Zoller, Controlled source of entangled photonic qubits, Phys. Rev. A 61, 062311, (2000-05-17), URL doi:10.1103/PhysRevA.61.062311 (ID: 337605) Toggle Abstract
We consider a general proposal for generating a train of entangled single-photon wavepackets. The photons are created inside a resonator via an interaction with an active medium. In the course of the generation process photons are transferred to the continuum outside the resonator through cavity loss. We show that wave packets generated in this way can be regarded as independent logical qubits. This and the possibility of producing strong entanglement between the qubits suggests many applications in quantum communication. We give a specific example in the context of cavity QED and show that undesired decoherence effects can be efficiently reduced in the considered scheme.
- L. Duan, G. Giedke, J. I. Cirac, P. Zoller, Inseparability Criterion for Continuous Variable Systems, Phys. Rev. Lett. 84, 2722, (2000-03-20), URL doi:10.1103/PhysRevLett.84.2722 (ID: 337606) Toggle Abstract
An inseparability criterion based on the total variance of a pair of Einstein-Podolsky-Rosen type operators is proposed for continuous variable systems. The criterion provides a sufficient condition for entanglement of any two-party continuous variable states. Furthermore, for all Gaussian states, this criterion turns out to be a necessary and sufficient condition for inseparability.
- L. Duan, G. Giedke, J. I. Cirac, P. Zoller, Entanglement Purification of Gaussian Continuous Variable Quantum States, Phys. Rev. Lett. 84, 4002, (2000-04-24), URL doi:10.1103/PhysRevLett.84.4002 (ID: 337607) Toggle Abstract
We describe an entanglement purification protocol to generate maximally entangled states with high efficiencies from two-mode squeezed states or from mixed Gaussian continuous entangled states. The protocol relies on a local quantum nondemolition measurement of the total excitation number of several continuous variable entangled pairs. We propose an optical scheme to do this kind of measurement using cavity enhanced cross-Kerr interactions.
- H. J. Briegel, T. Calarco, D. Jaksch, J. I. Cirac, P. Zoller, Quantum computing with neutral atoms, Journal of Modern Optics 47, 415, (2000-02-15), URL doi:10.1080/095003400148303 (ID: 337608) Toggle Abstract
We develop a method to entangle neutral atoms using cold controlled collisions. We analyse this method in two particular set-ups: optical lattices and magnetic microtraps. Both offer the possibility of performing certain multi-particle operations in parallel. Using this fact, we show how to implement efficient quantum error correction and schemes for fault-tolerant computing.
- P. Zoller, Quantum optics: Tricks with a single photon, Nature 404, 340, (2000-03-23), URL doi:10.1038/35006185 (ID: 337610)
- J. I. Cirac, P. Zoller, A scalable quantum computer with ions in an array of microtraps, Nature 404, 579, (2000-04-06), URL doi:10.1038/35007021 (ID: 337611) Toggle Abstract
Quantum computers require the storage of quantum information in a set of two-level systems (called qubits), the processing of this information using quantum gates and a means of final readout. So far, only a few systems have been identified as potentially viable quantum computer models—accurate quantum control of the coherent evolution is required in order to realize gate operations, while at the same time decoherence must be avoided. Examples include quantum optical systems (such as those utilizing trapped ions or neutral atoms, cavity quantum electrodynamics and nuclear magnetic resonance) and solid state systems (using nuclear spins, quantum dots and Josephson junctions). The most advanced candidates are the quantum optical and nuclear magnetic resonance systems, and we expect that they will allow quantum computing with about ten qubits within the next few years. This is still far from the numbers required for useful applications: for example, the factorization of a 200-digit number requires about 3,500 qubits, rising to 100,000 if error correction is implemented. Scalability of proposed quantum computer architectures to many qubits is thus of central importance. Here we propose a model for an ion trap quantum computer that combines scalability (a feature usually associated with solid state proposals) with the advantages of quantum optical systems (in particular, quantum control and long decoherence times).
- Gardiner, Crispin, P. Zoller, Quantum kinetic theory. V. Quantum kinetic master equation for mutual interaction of condensate and noncondensate, Phys. Rev. A 61, 033601, (2000-02-04), URL doi:10.1103/PhysRevA.61.033601 (ID: 337612) Toggle Abstract
A detailed quantum kinetic master equation is developed that couples the kinetics of a trapped condensate to the vapor of noncondensed particles. This generalizes previous work that treated the vapor as being undepleted.
- T. Calarco, E. A. Hinds, D. Jaksch, J. Schmiedmayer, J. I. Cirac, P. Zoller, Quantum gates with neutral atoms: Controlling collisional interactions in time-dependent traps, Phys. Rev. A 61, 022304, (2000-01-10), URL doi:10.1103/PhysRevA.61.022304 (ID: 337613) Toggle Abstract
We theoretically study specific schemes for performing a fundamental two-qubit quantum gate via controlled atomic collisions by switching microscopic potentials. In particular we calculate the fidelity of a gate operation for a configuration where a potential barrier between two atoms is instantaneously removed and restored after a certain time. Possible implementations could be based on microtraps created by magnetic and electric fields, or potentials induced by laser light.
- L. Santos, G. V. Shlyapnikov, P. Zoller, M. Lewenstein, Bose-Einstein Condensation in Trapped Dipolar Gases, Phys. Rev. Lett. 85, 1791, (2000-08-28), URL doi:10.1103/PhysRevLett.85.1791 (ID: 337602) Toggle Abstract
We discuss Bose-Einstein condensation in a trapped gas of bosonic particles interacting dominantly via dipole-dipole forces. We find that in this case the mean-field interparticle interaction and, hence, the stability diagram are governed by the trapping geometry. Possible physical realizations include ultracold heteronuclear molecules, or atoms with laser induced electric dipole moments.
- D. Jaksch, J. I. Cirac, P. Zoller, S. L. Rolston, R. Cote, M. Lukin, Fast Quantum Gates for Neutral Atoms, Phys. Rev. Lett. 85, 2208, (2000-09-04), URL doi:10.1103/PhysRevLett.85.2208 (ID: 337601) Toggle Abstract
We propose several schemes for implementing a fast two-qubit quantum gate for neutral atoms with the gate operation time much faster than the time scales associated with the external motion of the atoms in the trapping potential. In our example, the large interaction energy required to perform fast gate operations is provided by the dipole-dipole interaction of atoms excited to low-lying Rydberg states in constant electric fields. A detailed analysis of imperfections of the gate operation is given.
- L. J. Garay, J. R. Anglin, J. I. Cirac, P. Zoller, Sonic Analog of Gravitational Black Holes in Bose-Einstein Condensates, Phys. Rev. Lett. 85, 4643, (2000-11-27), URL doi:10.1103/PhysRevLett.85.4643 (ID: 337595) Toggle Abstract
It is shown that, in dilute-gas Bose-Einstein condensates, there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit a behavior resembling that of gravitational black holes. The dynamical instabilities involve creation of quasiparticle pairs in positive and negative energy states, as in the well-known suggested mechanism for black-hole evaporation. We propose a scheme to generate a stable sonic black hole in a ring trap.
- L. Duan, J. I. Cirac, P. Zoller, E. Polzik, Quantum Communication between Atomic Ensembles Using Coherent Light, Phys. Rev. Lett. 85, 005643, (2000-12-25), URL http://scitation.aip.org/jhtml/doi.jsp (ID: 337594) Toggle Abstract
Protocols for quantum communication between massive particles, such as atoms, are usually based on making use of nonclassical light, and/or superhigh finesse optical cavities are normally needed to enhance interaction between atoms and photons. We demonstrate a remarkable result: by using only coherent light, entanglement can be generated between distant free space atomic ensembles, and an unknown quantum state can thus be teleported from one to another. Neither nonclassical light nor cavities are needed in the scheme, which greatly simplifies its experimental implementation.
- L. Duan, A. Sorensen, J. I. Cirac, P. Zoller, Squeezing and Entanglement of Atomic Beams, Phys. Rev. Lett. 85, 3991, (2000-11-06), URL doi:10.1103/PhysRevLett.85.3991 (ID: 337596) Toggle Abstract
We propose and analyze a scheme for generating entangled atomic beams out of a Bose-Einstein condensate using spin-exchanging collisions. In particular, we show how to create both atomic squeezed states and entangled states of pairs of atoms.
- T. Calarco, H. J. Briegel, D. Jaksch, J. I. Cirac, P. Zoller, Quantum Computing with Trapped Particles in Microscopic Potentials, Fortschr. Phys. 48, 945, (2000-10-25), URL 10.1002/1521-3978(200009)48:9/11<945::AID-PROP945>3.0.CO;2-2 (ID: 337593) Toggle Abstract
We review recent proposals for performing entanglement manipulation via controlled interactions between trapped atoms. State-dependent, time-varying microscopic potentials allow one to obtain with high fidelity a conditional phase shift realizing a universal quantum gate. We discuss possible physical implementations with existing experimental techniques, for example optical lattices and magnetic micro-traps.
- D. Jaksch, T. Calarco, P. Zoller, Auf dem Weg zum universellen Quantencomputer, Physik in unserer Zeit 31, 260, (2000), URL (ID: 337597) Toggle Abstract
Die Quantenmechanik eröffnet faszinierende Perspektiven für die Kommunikation und die Informationsverarbeitung. Um universell programmierbare Quantenrechner realisieren zu können bedarf es der Implementierung von Konzepten zur Quanteninformationsverarbeitung die sich auf eine große Anzahl von Qubits anwenden lassen.
- J. F. Poyatos, J. I. Cirac, P. Zoller, Schemes of Quantum Computations with Trapped Ions, Fortschr. Phys. 48, 785, (2000), URL (ID: 337598) Toggle Abstract
The purpose of this article is to review two complementary schemes for quantum computation with trapped ions. We initially discuss the first proposal of quantum computations with cold trapped ions (J. I. Cirac and P. Zoller; Phys. Rev. Lett. 74, 4091, 1995) which requires, prior to any computation, laser cooling to the motional ground state. This proposal is closely related to the physics of generating and manipulating N-particles entangled states in both ion traps and high-Q cavities (cavity quantum electrodynamics). The second scheme is that of quantum computations with hot trapped ions (J.F. Poyatos, J.I. Cirac and P. Zoller; Phys. Rev. Lett. 81, 1322, 1998) which works at finite temperature and resembles physical ideas found in atom interferometry.
- T. Calarco, H. J. Briegel, D. Jaksch, J. I. Cirac, P. Zoller, Entangling neutral atoms for quantum information processing, Journal of Modern Optics 47, 2137, (2000-10-15), URL (ID: 337599) Toggle Abstract
We review recent proposals for performing entanglement manipulation via cold collisions between neutral atoms. State-dependent, time-varying trapping potentials allow one to control the interaction between atoms, so that conditional phase shifts realizing a universal quantum gate can be obtained with high fidelity. We discuss possible physical implementations with existing experimental techniques, for example optical lattices and magnetic micro-traps.
- L. Duan, G. Giedke, J. I. Cirac, P. Zoller, Physical implementation for entanglement purification of Gaussian continuous-variable quantum states, Phys. Rev. A 62, 32304, (2000-08-14), URL doi:10.1103/PhysRevA.62.032304 (ID: 337600) Toggle Abstract
We give a detailed description of the entanglement purification protocol which generates maximally entangled states with high efficiencies from realistic Gaussian continuous variable entangled states. The physical implementation of this protocol is extensively analyzed using high finesse cavities and cavity enhanced cross Kerr nonlinearities. In particular, we take into account many imperfections in the experimental scheme and calculate their influences. Quantitative requirements are given for the relevant experimental parameters.
- L. Duan, G. Giedke, J. I. Cirac, P. Zoller, Continuous variable entanglement purification and its physical implementation, Journal of Modern Optics 47, 2529, (2000-11-20), URL (ID: 337615) Toggle Abstract
We describe in detail an entanglement purification protocol which generates maximally entangled states with high efficiencies from realistic Gaussian continuous variable entangled states. A physical implementation of this protocol which uses high finesse cavities and cavity enhanced cross-Kerr nonlinearities is analysed.
- W. Dür, H. J. Briegel, J. I. Cirac, P. Zoller, Quantum repeaters based on entanglement purification, Phys. Rev. A 59, 000169, (1999-01-00), URL doi:10.1103/PhysRevA.59.169 (ID: 352427) Toggle Abstract
We study the use of entanglement purification for quantum communication over long distances. For distances much longer than the coherence length of a corresponding noisy quantum channel, the fidelity of transmission is usually so low that standard purification methods are not applicable. It is possible, however, to divide the channel into shorter segments that are purified separately and then connected by the method of entanglement swapping. This method can be much more efficient than schemes based on quantum error correction, as it makes explicit use of two-way classical communication. An important question is how the noise, introduced by imperfect local operations (that constitute the protocols of purification and the entanglement swapping), accumulates in such a compound channel, and how it can be kept below a certain noise level. To treat this problem, we first study the applicability and the efficiency of entanglement purification protocols in the situation of imperfect local operations. We then present a scheme that allows entanglement purification over arbitrary long channels and tolerates errors on the percent level. It requires a polynomial overhead in time, and an overhead in local resources that grows only logarithmically with the length of the channel.
- C. Cabrillo, J. I. Cirac, P. Garcia-Fernandez, P. Zoller, Creation of entangled states of distant atoms by interference, Phys. Rev. A 59, 001025, (1999-02-00), URL doi:10.1103/PhysRevA.59.1025 (ID: 352426) Toggle Abstract
We propose a scheme to create distant entangled atomic states. It is based on driving two (or more) atoms with a weak laser pulse, so that the probability that two atoms are excited is negligible. If the subsequent spontaneous emission is detected, the entangled state is created. We have developed a model to analyze the fidelity of the resulting state as a function of the dimensions and location of the detector, and the motional properties of the atoms.
- D. Jaksch, H. J. Briegel, J. I. Cirac, Gardiner, Crispin, P. Zoller, Entanglement of Atoms via Cold Controlled Collisions, Phys. Rev. Lett. 82, 001975, (1999-03-01), URL doi:10.1103/PhysRevLett.82.1975 (ID: 352425) Toggle Abstract
We show that by using cold controlled collisions between two atoms one can achieve conditional dynamics in moving trap potentials. We discuss implementing two qubit quantum gates and efficient creation of highly entangled states of many atoms in optical lattices.
- J. I. Cirac, P. Zoller, Engineering Entangled States of Trapped Ions, Physics World 01, (1999-01-00), (ID: 352424)
- G. Giedke, H. J. Briegel, J. I. Cirac, P. Zoller, Lower bounds for attainable fidelities in entanglement purification, Phys. Rev. A 59, 002641, (1999-04-00), URL doi:10.1103/PhysRevA.59.2641 (ID: 352423) Toggle Abstract
We derive lower bounds for the attainable fidelity of standard entanglement purification protocols when local operations and measurements are subjected to errors. We introduce an error parameter which measures the distance between the ideal completely positive map describing a purification step and the one in the presence of errors. We derive nonlinear maps for a lower bound of the fidelity at each purification step in terms of this parameter.
- G. Morigi, J. Eschner, J. I. Cirac, P. Zoller, Laser Cooling of two trapped ions: Sideband cooling beyond the Lamb-Dicke limit, Phys. Rev. A 59, 003793, (1999-05-00), URL doi:10.1103/PhysRevA.59.3797 (ID: 352422) Toggle Abstract
We study laser cooling of two ions that are trapped in a harmonic potential and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is shown to work analogously to sideband cooling of a single ion. Outside the Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes result in a quasicontinuous energy spectrum that significantly alters the cooling dynamics. The cooling time decreases nonlinearly with the linewidth of the cooling transition, and the effect of dark states which may slow down the cooling is considerably reduced. We show that cooling to the ground state is also possible outside the Lamb-Dicke regime. We develop the model and use quantum Monte Carlo calculations for specific examples. We show that a rate equation treatment is a good approximation in all cases.
- H. J. Kimble, J. I. Cirac, P. Zoller, Quantum communication with dark photons, Phys. Rev. A 59, 002659, (1999-04-00), URL doi:10.1103/PhysRevA.59.2659 (ID: 352421) Toggle Abstract
We show that quantum information may be transferred between atoms in different locations by using "phantom" or "dark" photons: the atoms are coupled through electromagnetic fields, but the corresponding field modes do not have to be fully populated. In the case where atoms are placed inside optical cavities, errors in quantum information processing due to photon absorption inside the cavity are diminished in this way. This effect persists up to intercavity distances of about a meter for the current levels of cavity losses, and may be useful for distributed quantum computing.
- G. Morigi, J. Eschner, J. I. Cirac, P. Zoller, Laser cooling of two trapped ions: Sideband cooling beyond the Lamb-Dicke limit, Phys. Rev. A 59, 3797, (1999), (ID: 344243) Toggle Abstract
We study laser cooling of two ions that are trapped in a harmonic potential and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is shown to work analogously to sideband cooling of a single ion. Outside the Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes result in a quasicontinuous energy spectrum that significantly alters the cooling dynamics. The cooling time
decreases nonlinearly with the linewidth of the cooling transition, and the effect of dark states which may slow down the cooling is considerably reduced. We show that cooling to the ground state is also possible outside the Lamb-Dicke regime. We develop the model and use quantum Monte Carlo calculations for specific examples. We show that a rate equation treatment is a good approximation in all cases.
- K. M. Gheri, P. Törmä, P. Zoller, Quantum state engineering with photonic qubits, Acta Physica Slovaca 49, 523, (1999), URL (ID: 352420) Toggle Abstract
We outline a scheme for the generation of a train of entangled single-photon wavepackets using standard CQED-techniques. The generated photons are transferred to the continuum outside the resonator through cavity loss in the form of wavepackets each of which may be regarded as a logical qubit. We show that undesired decoherence effects can be efficiently reduced in the considered scheme.
- H. J. Briegel, J. I. Cirac, P. Zoller, Quantencomputer: Wie sich Verschränkung für die Informationsverarbeitung nutzen lässt, Physikalische Blätter 55, 37, (1999), (ID: 537023)
- K. M. Gheri, K. Ellinger, T. Pellizzari, P. Zoller, Photon-Wavepackets as Flying Quantum Bits, Fortschr. Phys. 46, 401, (1998), URL (ID: 367773) Toggle Abstract
A novel description of the interaction of quantum optical systems with a single one-photon wave packet in terms of a generalized master equation is introduced. A corresponding quantum Monte-Carlo wavefunction simulation algorithm can be obtained from the driven system approach [H. J. Carmichael, Phys. Rev. Lett. 70, 2273 (1993); C. W. Gardiner, ibid. 2269 (1993)].
- H. J. Briegel, W. Dür, J. I. Cirac, P. Zoller, Quantum communication and the creation of maximally entangled pairs of atoms over a noisy channel, Phil. Trans. R. Soc. Lond. A 356, 1841, (1998-08-15), URL doi:10.1098/rsta.1998.0252 (ID: 367767) Toggle Abstract
We show how to create maximally entangled EPR pairs between spatially distant atoms, each of them inside a high-Q optical cavity, by sending photons through a general, noisy channel, such as a standard optical fiber. An error correction scheme that uses few auxiliary atoms in each cavity effectively eliminates photoabsorption and other transmission errors. This realizes the 'absorption free channel'. A concatenation protocol using the absorption free channel allows for quantum communication with single qubits over distances much larger than the coherence length of the channel.
- H. J. Briegel, W. Dür, J. I. Cirac, P. Zoller, Quantum Repeaters: The Role of Imperfect Local Operations in Quantum Communication, Phys. Rev. Lett. 81, 5932, (1998-12-26), URL doi:10.1103/PhysRevLett.81.5932 (ID: 367760) Toggle Abstract
In quantum communication via noisy channels, the error probability scales exponentially with the length of the channel. We present a scheme of a quantum repeater that overcomes this limitation. The central idea is to connect a string of (imperfect) entangled pairs of particles by using a novel nested purification protocol, thereby creating a single distant pair of high fidelity. Our scheme tolerates general errors on the percent level, it works with a polynomial overhead in time and a logarithmic overhead in the number of particles that need to be controlled locally.
- D. Jaksch, Gardiner, Crispin, K. M. Gheri, P. Zoller, Quantum kinetic theory. IV. Intensity and amplitude fluctuations of a Bose-Einstein condensate at finite temperature including trap loss, Phys. Rev. A 58, 1450, (1998-08-00), URL doi:10.1103/PhysRevA.58.1450 (ID: 367772) Toggle Abstract
We use the quantum kinetic theory to calculate the steady state and fluctuations of a trapped Bose-Einstein condensate at a finite temperature. The system is divided in a condensate and a noncondensate part. A quantum-mechanical description based on the number-conserving Bogoliubov method is used for describing the condensate part. The noncondensed particles are treated as a classical gas in thermal equilibrium with temperature T and chemical potential μ. We find a master equation for the reduced density operator of the Bose-Einstein condensate, calculate the steady state of the system, and investigate the effect of one-, two-, and three-particle losses on the condensate. Using linearized Ito equations, we find expressions for the intensity fluctuations and the amplitude fluctuations in the condensate. A Lorentzian line shape is found for the intensity correlation function that is characterized by a time constant γI-1 derived in the paper. For the amplitude correlation function, we find ballistic behavior for time differences smaller than γI-1, and diffusive behavior for larger time differences.
- J. F. Poyatos, J. I. Cirac, P. Zoller, Quantum Gates with “Hot” Trapped Ions, Phys. Rev. Lett. 81, 1322, (1998-08-10), URL doi:10.1103/PhysRevLett.81.1322 (ID: 367770) Toggle Abstract
We propose a scheme to perform a fundamental two-qubit gate between two trapped ions using ideas from atom interferometry. As opposed to the scheme considered by J. I. Cirac and P. Zoller, [Phys. Rev. Lett. 74, 4091 (1995)], it does not require laser cooling to the motional ground state.
- Gardiner, Crispin, P. Zoller, Quantum kinetic theory. III. Quantum kinetic master equation for strongly condensed trapped systems, Phys. Rev. A 58, 536, (1998-07-00), URL doi:10.1103/PhysRevA.58.536 (ID: 367769) Toggle Abstract
We extend quantum kinetic theory to deal with a strongly Bose-condensed atomic vapor in a trap. The method assumes that the majority of the vapor is not condensed, and acts as a bath of heat and atoms for the condensate. The condensate is described by the particle-number-conserving Bogoliubov method developed by one of the authors. We derive equations which describe the fluctuations of particle number and phase, and the growth of the Bose-Einstein condensate. The equilibrium state of the condensate is a mixture of states with different numbers of particles and quasiparticles. It is not a quantum superposition of states with different numbers of particles—nevertheless, the stationary state exhibits the property of off-diagonal long-range order, to the extent that this concept makes sense in a tightly trapped condensate.
- J. I. Cirac, P. Zoller, H. J. Kimble, H. Mabuchi, Quantum Communication in a Quantum Network, Physica Scripta T76, 223, (1998), URL (ID: 367768) Toggle Abstract
We propose a physical implementation for quantum communication in quantum networks. Our scheme demonstrates how to transfer quantum information between spatially separated atoms, which are each inside a high-Q optical cavity, and how to establish a distant maximally entangled pair, by sending photons through a general, noisy channel, such as a standard optical fiber.
- K. M. Gheri, C. Saavedra, P. Törmä, J. I. Cirac, P. Zoller, Entanglement engineering of one-photon wave packets using a single-atom source, Phys. Rev. A 58, R2627, (1998-10-00), URL doi:10.1103/PhysRevA.58.R2627 (ID: 367766) Toggle Abstract
We propose a cavity-QED scheme for the controlled generation of sequences of entangled single-photon wave packets. A photon is created inside a cavity via an active medium, such as an atom, and decays into the continuum of radiation modes outside the cavity. Subsequent wave packets generated in this way behave as independent logical quantum bits (qubits). This and the possibility of producing maximally entangled multiqubit states suggest many applications in quantum communication.
- D. Jaksch, C. Bruder, J. I. Cirac, Gardiner, Crispin, P. Zoller, Cold Bosonic Atoms in Optical Lattices, Phys. Rev. Lett. 81, 3108, (1998-10-12), URL doi:10.1103/PhysRevLett.81.3108 (ID: 367764) Toggle Abstract
The dynamics of an ultracold dilute gas of bosonic atoms in an optical lattice can be described by a Bose-Hubbard model where the system parameters are controlled by laser light. We study the continuous (zero temperature) quantum phase transition from the superfluid to the Mott insulator phase induced by varying the depth of the optical potential, where the Mott insulator phase corresponds to a commensurate filling of the lattice (“optical crystal”). Examples for formation of Mott structures in optical lattices with a superimposed harmonic trap and in optical superlattices are presented.
- Gardiner, Crispin, M. D. Lee, R. J. Ballagh, M. J. Davis, P. Zoller, Quantum Kinetic Theory of Condensate Growth: Comparison of Experiment and Theory, Phys. Rev. Lett. 81, 5266, (1998-12-14), URL doi:10.1103/PhysRevLett.81.5266 (ID: 367762) Toggle Abstract
In a major extension of our previous model [Phys. Rev. Lett. 79, 1793 (1997)] of condensate growth, we take account of the evolution of the occupations of lower trap levels, and of the full Bose-Einstein formula for the occupations of higher trap levels. We find good agreement with experiment, especially at higher temperatures. We also confirm the picture of the "kinetic" region of evolution, introduced by Kagan et al., for the time up to the initiation of the condensate. The behavior after initiation essentially follows our original growth equation, but with a substantially increased rate coefficient W^+.
- T. Busch, J. R. Anglin, J. I. Cirac, P. Zoller, Inhibition of spontaneous emission in Fermi gases, Europhys. Lett. 44, 1, (1998-08-10), URL doi:10.1209/epl/i1998-00426-2 (ID: 367757) Toggle Abstract
Fermi inhibition is a quantum-statistical analogue for the inhibition of spontaneous emission by an excited atom in a cavity. This is achieved when the relevant motional states are already occupied by a cloud of cold atoms in the internal ground state. We exhibit non-trivial effects at finite temperature and in anisotropic traps, and briefly consider a possible experimental realization.
- G. Morigi, J. I. Cirac, K. Ellinger, P. Zoller, Laser cooling of trapped atoms to the ground state: A dark state in position space, Phys. Rev. A 57, 2909, (1998-04-00), URL doi:10.1103/PhysRevA.57.2909 (ID: 367774) Toggle Abstract
We propose a scheme that allows us to laser cool trapped atoms to the ground state of a one-dimensional confining potential. The scheme is based on the creation of a dark state by designing the laser profile, so that the hottest atoms are coherently pumped to another internal level, and then repumped back. The scheme works beyond the Lamb-Dicke limit. We present results of a full quantum treatment for a one-dimensional model.
- J. I. Cirac, M. Lewenstein, K. Moelmer, P. Zoller, Quantum superposition states of Bose-Einstein condensates, Phys. Rev. A 57, 1208, (1998-02-00), URL doi:10.1103/PhysRevA.57.1208 (ID: 367775) Toggle Abstract
We propose a scheme to create a macroscopic "Schrödinger-cat" state formed by two interacting Bose condensates. In analogy with quantum optics, where the control and engineering of quantum states can be maintained to a large extent, we consider the present scheme to be an example of quantum atom optics at work.
- P. Zoller, H. J. Kimble, H. Mabuchi, Transmission of quantum information in a quantum network: A quantum optical implementation, Fortschr. Phys. 46, 689, (1998), URL (ID: 367803) Toggle Abstract
We show how to transmit quantum communication reliably between the nodes of a quantum network. The nodes are represented by atoms, stored in a trap. The communication is accomplished via photons, which are coupled to the atoms by a high-Q cavity. We discuss the effects of decoherence and ways to correct for the corresponding errors.
- J. F. Poyatos, J. I. Cirac, P. Zoller, Characterization of decoherence processes in quantum computation, Optics Express 2, 372, (1998), (ID: 367802)
- P. Zoller, Photonic Channels for Quantum Communication, Science 279, 205, (1998-01-09), URL doi:10.1126/science.279.5348.205 (ID: 367794) Toggle Abstract
A general photonic channel for quantum communication is defined. By means of local quantum computing with a few auxiliary atoms, this channel can be reduced to one with effectively less noise. A scheme based on quantum interference is proposed that iteratively improves the fidelity of distant entangled particles.
- J. I. Cirac, P. Zoller, Quantenkommunikation und Quantencomputing, Mitteilungsblatt d. Österr. Physikal. Ges. 1, (1998), URL (ID: 367793)
- N. Lütkenhaus, J. I. Cirac, P. Zoller, Mimicking a squeezed-bath interaction: Quantum-reservoir engineering with atoms, 57, 548, (1998-01-00), URL doi:10.1103/PhysRevA.57.548 (ID: 367777) Toggle Abstract
The interaction of an atomic two-level system and a squeezed vacuum leads to interesting effects in atomic dynamics, including line narrowing in resonance fluorescence and absorption spectra, and a suppressed (enhanced) decay of the in-phase and out-of-phase components of the atomic polarization. On the experimental side these predictions have so far eluded observation, essentially due to the difficulty of embedding atoms in a 4 pi squeezed vacuum. In this paper we show how to "engineer" a squeezed-bath-type interaction for an effective two-level system. In the simplest example, our two-level atom is represented by the two ground levels of an atom with an angular momentum J = 1/2 --> J = 1/2 transition (a four-level system), which is driven by (weak) laser fields and coupled to the vacuum reservoir of radiation modes. Interference between the spontaneous emission channels in optical pumping leads to a squeezed-bath-type coupling and thus to symmetry breaking of decay on the Bloch sphere. With this system it should be possible to observe the effects predicted in the context of squeezed-bath–atom interactions. The laser parameters allow one to choose properties of the squeezed-bath interaction, such as the (effective) photon-number expectation number N and the squeezing phase phi. We present results of a detailed analytical and numerical study.
- R. Dumhart, J. I. Cirac, M. Lewenstein, P. Zoller, Creation of Dark Solitons and Vortices in Bose-Einstein Condensates, Phys. Rev. Lett. 80, 2972, (1998-04-06), URL doi:10.1103/PhysRevLett.80.2972 (ID: 367776) Toggle Abstract
We propose and analyze a scheme to create dark solitons and vortices in Bose-Einstein condensates. This is achieved starting from a condensate in the internal state |a> and transferring the atoms to the internal state |b> via a Raman transition induced by laser light. By scanning adiabatically the Raman detuning, dark solitons and vortices are created.
- J. F. Poyatos, J. I. Cirac, P. Zoller, Complete Characterization of a Quantum Process: The Two-Bit Quantum Gate, Phys. Rev. Lett. 78, 390, (1997-01-13), URL doi:10.1103/PhysRevLett.78.390 (ID: 367817) Toggle Abstract
We show how to fully characterize a quantum process in an open quantum system. We particularize the procedure to the case of a universal two-qubit gate in a quantum computer. We illustrate the method with a numerical simulation of a quantum gate in the ion trap quantum computer.
- H. Stecher, H. Ritsch, P. Zoller, F. Sander, T. Esslinger, T. W. Hänsch, All-optical gray lattice for atoms, Phys. Rev. A 55, 545, (1997-01-00), URL doi:10.1103/PhysRevA.55.545 (ID: 367816) Toggle Abstract
We create a gray optical lattice structure using a blue detuned laser field coupling an atomic ground state of angular momentum J simultaneously to two excited states with angular momenta J and J – 1. The atoms are cooled and trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest-energy band, which is only weakly coupled to the light field. Very low kinetic temperatures are obtained by adiabatically reducing the optical potential. The dynamics of this process is analyzed using a full quantum Monte Carlo simulation. The calculations explicitly show the mapping of the band populations on the corresponding momentum intervals of the free atom. In an experiment with subrecoil momentum resolution we measure the band populations and find excellent absolute agreement with the theoretical calculations.
- S. Gardiner, J. I. Cirac, P. Zoller, Nonclassical states and measurement of general motional observables of a trapped ion, Phys. Rev. A 55, 1683, (1997-03-00), URL doi:10.1103/PhysRevA.55.1683 (ID: 367815) Toggle Abstract
We describe a method to perform a single quantum measurement of an arbitrary motional observable of a single ion moving in a harmonic potential. We illustrate the measurement procedure with explicit examples, namely the position and phase observables. A necessary tool for this is the ability to synthesize an arbitrary motional state. In addition, we show how to generalize this to higher dimensions, and show explicit examples of how to engineer states in two spatial dimensions, including a proposed experimental configuration.
- J. I. Cirac, P. Zoller, H. J. Kimble, H. Mabuchi, Quantum State Transfer and Entanglement Distribution among Distant Nodes in a Quantum Network, Phys. Rev. Lett. 78, 3221, (1997-04-21), URL doi:10.1103/PhysRevLett.78.3221 (ID: 367814) Toggle Abstract
We propose a scheme to utilize photons for ideal quantum transmission between atoms located at spatially separated nodes of a quantum network. The transmission protocol employs special laser pulses that excite an atom inside an optical cavity at the sending node so that its state is mapped into a time-symmetric photon wave packet that will enter a cavity at the receiving node and be absorbed by an atom there with unit probability. Implementation of our scheme would enable reliable transfer or sharing of entanglement among spatially distant atoms.
- G. Morigi, J. I. Cirac, M. Lewenstein, P. Zoller, Ground-state laser cooling beyond the Lamb-Dicke limit, Europhys. Lett. 39, 13, (1997-05-26), URL doi:10.1209/epl/i1997-00306-3 (ID: 367813) Toggle Abstract
We propose a laser cooling scheme that allows to cool a single atom confined in a harmonic potential to the trap ground state |0>. The scheme assumes strong confinement, where the oscillation frequency in the trap is larger than the effective spontaneous decay width, but is not restricted to the Lamb-Dicke limit, i.e. the size of the trap ground state can be larger than the optical wavelength. This cooling scheme may be useful in the context of quantum computations with ions and Bose-Einstein condensation.
- S. van Enk, J. I. Cirac, P. Zoller, Ideal Quantum Communication over Noisy Channels: A Quantum Optical Implementation, Phys. Rev. Lett. 78, 4293, (1997-06-02), URL doi:10.1103/PhysRevLett.78.4293 (ID: 367812) Toggle Abstract
We consider transmission of a quantum state between two distant atoms via photons. Based on a quantum-optical realistic model, we define a noisy quantum channel which includes systematic errors as well as errors due to coupling to the environment. We present a protocol that allows one to accomplish ideal transmission by repeating the transfer operation as many times as needed.
- Gardiner, Crispin, P. Zoller, Quantum kinetic theory: A quantum kinetic master equation for condensation of a weakly interacting Bose gas without a trapping potential, Phys. Rev. A 55, 2902, (1997-04-00), URL doi:10.1103/PhysRevA.55.2902 (ID: 367811) Toggle Abstract
A quantum kinetic master equation (QKME) for bosonic atoms is formulated. It is a quantum stochastic equation for the kinetics of a dilute quantum Bose gas, and describes the behavior and formation of Bose condensation. The key assumption in deriving the QKME is a Markov approximation for the atomic collision terms. In the present paper the basic structure of the theory is developed, and approximations are stated and justified to delineate the region of validity of the theory. Limiting cases of the QKME include the quantum Boltzmann master equation and the Uehling-Uhlenbeck equation, as well as an equation analogous to the Gross-Pitaevskii equation.
- D. Jaksch, Gardiner, Crispin, P. Zoller, Quantum kinetic theory. II. Simulation of the quantum Boltzmann master equation, Phys. Rev. A 56, 575, (1997-07-00), URL doi:10.1103/PhysRevA.56.575 (ID: 367810) Toggle Abstract
We present results of simulations of a quantum Boltzmann master equation (QBME) describing the kinetics of a dilute Bose gas confined in a trapping potential in the regime of Bose condensation. The QBME is the simplest version of a quantum kinetic master equation derived in previous work. We consider two cases of trapping potentials: a three-dimensional square-well potential with periodic boundary conditions and an isotropic harmonic oscillator. We discuss the stationary solutions and relaxation to equilibrium. In particular, we calculate particle distribution functions, fluctuations in the occupation numbers, the time between collisions, and the mean occupation numbers of the one-particle states in the regime of onset of Bose condensation.
- V. M. Perez-Garcia, H. Michinel, J. I. Cirac, M. Lewenstein, P. Zoller, Dynamics of Bose-Einstein condensates: Variational solutions of the Gross-Pitaevskii equations, Phys. Rev. A 56, 1424, (1997-08-00), URL doi:10.1103/PhysRevA.56.1424 (ID: 367809) Toggle Abstract
A variational technique is applied to solve the time-dependent nonlinear Schrödinger equation (Gross-Pitaevskii equation) with the goal to model the dynamics of dilute ultracold atom clouds in the Bose-Einstein condensed phase. We derive analytical predictions for the collapse, equilibrium widths, and evolution laws of the condensate parameters and find them to be in very good agreement with our numerical simulations of the nonlinear Schrödinger equation. It is found that not only the number of particles, but also both the initial width of the condensate and the effect of different perturbations to the condensate may play a crucial role in the collapse dynamics. The results are applicable when the shape of the condensate is sufficiently simple.
- Gardiner, Crispin, P. Zoller, R. J. Ballagh, M. J. Davis, Kinetics of Bose-Einstein Condensation in a Trap, Phys. Rev. Lett. 79, 1793, (1997-09-08), URL doi:10.1103/PhysRevLett.79.1793 (ID: 367808) Toggle Abstract
The formation process of a Bose-Einstein condensate in a trap is described using a master equation based on quantum kinetic theory, which can be well approximated by a description using only the condensate mode in interaction with a thermalized bath of noncondensate atoms. A rate equation of the form n-dot = 2W+(n)[(1–exp((µn–µ)/kT))n + 1] is derived, in which the difference between the condensate chemical potential µn and the bath chemical potential µ gives the essential behavior. Solutions of this equation give a characteristic latency period for condensate formation and appear to be consistent with the observed behavior of both rubidium and sodium condensate formation.
- T. Busch, J. I. Cirac, V. M. Perez-Garcia, P. Zoller, Stability and collective excitations of a two-component Bose-Einstein condensed gas: A moment approach, Phys. Rev. A 56, 2978, (1997-10-04), URL doi:10.1103/PhysRevA.56.2978 (ID: 367807) Toggle Abstract
The dynamics of a two-component dilute Bose-Einstein gas of atoms at zero temperature is described in the mean-field approximation by a two-component Gross-Pitaevskii equation. We solve this equation assuming a Gaussian shape for the wave function, where the free parameters of the trial wave function are determined using a moment method. We derive equilibrium states and the phase diagrams for the stability for positive and negative s-wave scattering lengths, and obtain the low-energy excitation frequencies corresponding to the collective motion of the two Bose-Einstein condensates.
- S. van Enk, J. I. Cirac, P. Zoller, Purifying Two-Bit Quantum Gates and Joint Measurements in Cavity QED, Phys. Rev. Lett. 79, 5178, (1997-12-22), URL doi:10.1103/PhysRevLett.79.5178 (ID: 367806) Toggle Abstract
Using a cavity QED setup we show how to implement a particular joint measurement on two atoms in a fault tolerant way. Based on this scheme, we illustrate how to realize quantum communication over a noisy channel when local operations are subject to errors. We also present a scheme to perform and purify a fundamental two-bit gate.
- J. I. Cirac, P. Zoller, H. J. Kimble, H. Mabuchi, Quantum state transfer in a quantum network: a quantum-optical implementation, J. Mod. Opt. 44, 1727, (1997-10-01), URL doi:10.1080/095003497152762 (ID: 367805) Toggle Abstract
We propose a scheme to utilize photons for ideal quantum transmission between atoms located at spatially separated nodes of a quantum network. We also propose a method to correct errors during transmission.
- S. Gardiner, J. I. Cirac, P. Zoller, Quantum Chaos in an Ion Trap: The Delta-Kicked Harmonic Oscillator, Phys. Rev. Lett. 79, 4790, (1997-12-15), URL doi:10.1103/PhysRevLett.79.4790 (ID: 367800) Toggle Abstract
We propose an experimental configuration, within an ion trap, by which a quantum mechanical delta-kicked harmonic oscillator could be realized, and investigated. We show how to directly measure the sensitivity of the ion motion to small variations in the external parameters.
- V. M. Perez-Garcia, H. Michinel, J. I. Cirac, M. Lewenstein, P. Zoller, Low Energy Excitations of a Bose-Einstein Condensate: A Time-Dependent Variational Analysis, Phys. Rev. Lett. 77, 005320, (1996), URL doi:10.1103/PhysRevLett.77.5320 (ID: 305704) Toggle Abstract
We solve the time-dependent Gross-Pitaevskii equation by a variational ansatz to calculate the excitation spectrum of a Bose-Einstein condensate in a trap. The trial wave function is a Gaussian which allows an essentially analytical treatment of the problem. Our results reproduce numerical calculations over the whole range from small to large particle numbers, and agree exactly with the Stringari results in the strong interaction limit. Excellent agreement is obtained with the recent JILA experiment and predictions for the negative scattering length case are also made.
- J. F. Poyatos, R. Walser, J. I. Cirac, R. Blatt, P. Zoller, Motion tomography of a single trapped ion, Phys. Rev. A 53, R1966, (1996), (ID: 344250)
- R. Blatt, P. Zoller, Quantengatter für Quantenrechner, Physikalische Blätter 52, 205, (1996), (ID: 344248)
- J. I. Cirac, Gardiner, Crispin, M. Naraschewski, P. Zoller, Continuous observation of interference fringes from Bose condensates, Phys. Rev. A 54, R3714–R3717, (1996), URL doi:10.1103/PhysRevA.54.R3714 (ID: 305685) Toggle Abstract
We use continuous measurement theory to describe the evolution of two Bose condensates in an interference experiment. It is shown how in a single run the system evolves into a state with a fixed relative phase, without violating particle number conservation.
- J. I. Cirac, A. S. Parkins, R. Blatt, P. Zoller, Non-Classical States of Motion in Ion Traps, Adv. Atom. Molec. and Opt. Physics 37, 238-296, (1996), (ID: 619592)
- J. F. Poyatos, J. I. Cirac, P. Zoller, Quantum Reservoir Engineering with Laser Cooled Trapped Ions, Phys. Rev. Lett. 77, 004728, (1996), URL doi:10.1103/PhysRevLett.77.4728 (ID: 305700) Toggle Abstract
We show how to design different couplings between a single ion trapped in a harmonic potential and an environment. The coupling is due to the absorption of a laser photon and subsequent spontaneous emission. The variation of the laser frequencies and intensities allows one to ``engineer'' the coupling and select the master equation describing the motion of the ion.
- J. F. Poyatos, R. Walser, J. I. Cirac, P. Zoller, Motion tomography of a single trapped ion, Phys. Rev. A 53, R1966–R1969, (1996), URL doi:10.1103/PhysRevA.53.R1966 (ID: 305687) Toggle Abstract
A method for the experimental reconstruction of the quantum state of motion for a single trapped ion is proposed. It is based on the measurement of the ground-state population of the trap after a sudden change of the trapping potential. In particular, we show how the Q( alpha ) function and the quadrature distribution P(x, theta ) can be measured directly. In an example we demonstrate the principle and analyze the sensitivity of the reconstruction process to experimental uncertainties as well as to finite grid limitations. Our method is not restricted to the Lamb-Dicke Limit and works in one or more dimensions.
- R. Walser, J. I. Cirac, P. Zoller, Magnetic Tomography of a Cavity State, Phys. Rev. Lett. 77, 002658, (1996), URL 10.1103/PhysRevLett.77.2658 (ID: 305684) Toggle Abstract
A method to determine the state of a single quantized cavity mode is proposed. By adiabatic passage, the quantum state of the field is transferred completely onto an internal Zeeman submanifold of an atom. Utilizing a method of Newton and Young [Ann. Phys. 49, 393 (1968)], we can determine this angular momentum state uniquely, by a finite number of magnetic dipole measurements with Stern-Gerlach analyzers. An example illustrates the influence of dissipation.
- M. Naraschewski, H. Wallis, A. Schenzle, J. I. Cirac, P. Zoller, Interference of Bose condensates, Phys. Rev. A 54, 2185–2196, (1996), URL doi:10.1103/PhysRevA.54.2185 (ID: 305682) Toggle Abstract
We investigate the prospects of atomic interference using samples of Bose condensed atoms. First we show the ability of two independent Bose condensates to create an interference pattern. This holds even if both condensates are described by Fock states. Thus, the existence of an experimental signature for a broken gauge symmetry, seen in a single run of the experiment, is not necessarily reflected by a broken symmetry on the level of the quantum mechanical state vector. Based on these results, we simulate numerically a recent experiment with two independent Bose condensates [K. B. Davis et al., Phys. Rev. Lett. 75, 3969 (1995)]. The existence of interference fringes is predicted based on the nonlinear Schrödinger equation. Finally we study theoretically the influence of finite temperatures on the visibility of the interference in a double pinhole configuration.
- J. F. Poyatos, J. I. Cirac, R. Blatt, P. Zoller, Trapped ions in the strong excitation regime: ion interferometry and non-classical states, Phys. Rev. A 54, 1532, (1996), (ID: 344249)
- J. I. Cirac, M. Lewenstein, P. Zoller, Laser cooling a trapped atom in a cavity: Bad-cavity limit, Phys. Rev. A 51, 1650–1655, (1995), URL doi:10.1103/PhysRevA.51.1650 (ID: 305621) Toggle Abstract
We analyze theoretically a one-dimensional model of laser cooling of an atom or ion trapped in a cavity. We assume that the cavity loss rate is much larger than the atom-cavity coupling (bad-cavity limit) and that the atomic excited state is weakly occupied (low saturation limit). After elimination of the cavity mode and the atomic excited state, we derive rate equations for the populations of the trap states. We find that in the Lamb-Dicke limit the atom can be cooled to the ground state of the trap even in the strong confinement limit. This result is interpreted in terms of quantum interferences between different cooling and heating processes involving spontaneous emission in the cavity.
- J. I. Cirac, M. Lewenstein, P. Zoller, Generalized Bose-Einstein distributions and multistability of a laser-cooled gas, Phys. Rev. A 51, 2899–2907, (1995), URL doi:10.1103/PhysRevA.51.2899 (ID: 305618) Toggle Abstract
We study the dynamics of a system of atoms undergoing laser cooling in a microtrap. Using a simple model, we show that the stationary state of the system can be different from the standard Bose-Einstein distribution. In particular, it can exhibit infinite sequences of phase transitions as a function of laser detuning, as well as multistable behavior. This is due to the combination of quantum statistical phenomena and other effects related to the laser-cooling process.
- J. I. Cirac, P. Zoller, Quantum Computations with Cold Trapped Ions, Phys. Rev. Lett. 74, 4091–4094, (1995), URL doi:10.1103/PhysRevLett.74.4091 (ID: 305614) Toggle Abstract
A quantum computer can be implemented with cold ions confined in a linear trap and interacting with laser beams. Quantum gates involving any pair, triplet, or subset of ions can be realized by coupling the ions through the collective quantized motion. In this system decoherence is negligible, and the measurement (readout of the quantum register) can be carried out with a high efficiency.
- M. Lewenstein, J. I. Cirac, P. Zoller, Master equation for sympathetic cooling of trapped particles, Phys. Rev. A 51, 4617–4627, (1995), URL doi:10.1103/PhysRevA.51.4617 (ID: 305613) Toggle Abstract
A model for cooling a system of bosons in a harmonic trap via their interactions with a thermal bath of other particles is studied. The master equation describing the evolution of the system is derived for an arbitrary number of spatial dimensions. This equation is characterized by transition rates between trap levels. We present an analytic approximation for these rates and compare it with exact formulas, derived for the case of an even number of spatial dimensions. Analytic expressions show very good agreement with the exact ones for a wide range of parameters. We also discuss the cooling dynamics in terms of the approximated rates.
- L. You, J. Cooper, P. Zoller, Quantum-classical correspondences for atomic operators: a positive presentation approach, JOSA B 12, 1774, (1995), URL (ID: 303476)
- T. Pellizzari, P. Marte, P. Zoller, Laser cooling to a single quantum state in a trap: One-dimensional results, Phys. Rev. A 52, 4709–4718, (1995), URL doi:10.1103/PhysRevA.52.4709 (ID: 303487) Toggle Abstract
Laser cooling in a trap is investigated for laser and trapping configurations which allow the existence of approximate ``dark states´´ of the combined atom-plus-trap system, i.e., states that are decoupled from the laser light by quantum interference. We show that a one-dimensional (1D) free-particle dark state in angular momentum Jg=1 to Je=1 transitions and in two counterpropagating laser fields survives as an approximate dark state in a ``flat-bottom´´ trap of size much larger than the optical wavelength. Furthermore, we show the existence of approximate dark states in 1D harmonic-oscillator potentials. In the latter configuration we are able to provide analytical results.
- S. Marksteiner, R. Walser, P. Marte, P. Zoller, Localization of atoms in light fields: Optical molasses, adiabatic compression and squeezing, Applied Physics B: Lasers and Optics 60, 145 - 153, (1995), URL doi:10.1007/BF01135856 (ID: 303542) Toggle Abstract
We present a theoretical study of the localization1 of atoms with an angular momentumJ g=3 toJ e=4 transition (e.g., chromium atoms) in quantized optical molasses created by two counterpropagating linearly polarized laser beams. We study the localization as a function of the potential depth, the angle between the polarizations and the interaction time with the molasses in the low-intensity limit, and discuss the possibility of adiabatic compression and squeezing of the atomic distribution.
- A. S. Parkins, P. Marte, P. Zoller, O. Carnal, H. J. Kimble, Quantum-state mapping between multilevel atoms and cavity light fields, Phys. Rev. A 51, 1578–1596, (1995), URL doi:10.1103/PhysRevA.51.1578 (ID: 303497) Toggle Abstract
A scheme for the preparation of Fock states and general superposition states of the electromagnetic field in a cavity is studied in detail. The scheme uses adiabatic passage in a strongly coupled atom-cavity system to ``map´´ atomic ground-state Zeeman coherence onto the cavity-mode field. We model photon-counting and homodyne measurements of the field exiting the cavity and demonstrate the possibility of generating and detecting highly nonclassical states of the field parameter values close to currently realizable experimental values. The adiabatic passage process is also reversible, enabling cavity-mode fields to be mapped onto atomic ground-state Zeeman coherence. Application of this property to the measurement of cavity fields is discussed, with particular consideration given to a possible scheme for quantum measurements of the intracavity photon number.
- T. Pellizzari, S. Gardiner, J. I. Cirac, P. Zoller, Decoherence, continuous observation, and quantum computing: a cavity qed model, Phys. Rev. Lett. 75, 3788–3791, (1995), URL doi:10.1103/PhysRevLett.75.3788 (ID: 303489) Toggle Abstract
We use the theory of continuous measurement to analyze the effects of decoherence on a realistic model of a quantum computer based on cavity QED. We show how decoherence affects the computation, and methods to prevent it.
- R. Blatt, J. I. Cirac, A. S. Parkins, P. Zoller, Quantum motion of trapped ions, Physica Scripta T59, 294, (1995), (ID: 305661)
- R. Blatt, J. I. Cirac, P. Zoller, Trapping states of motion with cold ions, Phys. Rev. A 52, 518–524, (1995), URL doi:10.1103/PhysRevA.52.518 (ID: 305623) Toggle Abstract
We describe a simple technique to prepare Fock states of the motion of an atom trapped in a harmonic potential. The method is based on using two lasers which interact with a weak and strong transition of the atom successively. Application of a well-defined pulse length on the weak transition leaves the population of some states out of the oscillator manifold unchanged (trapping states). Interaction on the strong transition with a second laser is used to repopulate one of these states via a third intermediate level.
- L. S. Goldner, C. Gerz, S. L. Rolston, C. I. Westbrook, W. D. Phillips, P. Marte, P. Zoller, Momentum transfer in laser-cooled cesium by adiabatic passage in a light field, Physical Review Letters 97, 997–1000, (1994-02-07), URL doi:10.1103/PhysRevLett.72.997 (ID: 375179) Toggle Abstract
We have observed transfer of momentum and ground state population in laser-cooled cesium by adiabatic following of a slowly evolving light field. In this new technique for mechanical manipulation of atoms, spontaneous emission is suppressed since the atoms evolve in a ‘‘dark’’ state that follows the light field. This means that the phase coherence of the atom is preserved so that this technique is useful in the realization of coherent atomic beam splitters and mirrors. Our experimental results are in good agreement with optical Bloch equation calculations.
©1994 The American Physical Society
- J. I. Cirac, A. Schenzle, P. Zoller, Inhibition of quantum tunneling of an atom due to the continuous observation of light scattering, Europhys. Lett. 27, 123, (1994), (ID: 375184)
- J. I. Cirac, M. Lewenstein, P. Zoller, Quantum statistics of a laser cooled ideal gas, Physical Review Letters 72, 2977–2980, (1994-05-09), URL doi:10.1103/PhysRevLett.72.2977 (ID: 375183) Toggle Abstract
We study the dynamics of a system of bosonic or fermionic atoms in a microscopic trap undergoing laser cooling. We show that the stationary state can be described by a Bose-Einstein or Fermi-Dirac distribution, respectively. Fluorescence from the system reflects quantum statistical properties.
©1994 The American Physical Society
- J. I. Cirac, P. Zoller, Preparation of macroscopic superpositions in many-atom systems, Phys. Rev. A 50, R2799–R2802, (1994-10-04), URL doi:10.1103/PhysRevA.50.R2799 (ID: 375182) Toggle Abstract
We propose a technique to prepare two or more atoms in certain entangled states, based on the interaction of the atoms with a cavity mode. After the atomic state is prepared, the cavity mode is left in the vacuum state, so dissipation does not affect the generated entangled states. These states could be used for improved tests that challenge local realistic theories, and to examine related phenomena, which, thus far, have been realized only with photons.
©1994 The American Physical Society
- R. Dumhart, P. Marte, T. Pellizzari, P. Zoller, Laser Cooling to a Single Quantum State in a Trap, Physical Review Letters 73, 2829–2832, (1994-11-21), URL doi:10.1103/PhysRevLett.73.2829 (ID: 375181) Toggle Abstract
Laser cooling in a trap is investigated for configurations which allow the existence of "dark states" of the combined atom-plus-trap system, i.e., states which are decoupled from the laser light by quantum interference. Two examples of approximate dark states in a 1D flat bottom and 2D harmonic trap for angular momentum 1 to 1 transitions are discussed. A wave function simulation of the quantum master equation predicts that a significant fraction of the atoms are transferred to a single trap state.
©1994 The American Physical Society
- K. Ellinger, J. Cooper, P. Zoller, Light-pressure force in N-atom systems, Phys. Rev. A 49, 3909–3933, (1994-05-05), URL doi:10.1103/PhysRevA.49.3909 (ID: 375180) Toggle Abstract
An analytical description of long-range collisions between atoms in a laser cooling field is developed. We begin by considering an N-atom master equation. In the regime of low atomic densities (i.e., where the mean distance between two atoms is much larger than the laser wavelength) it is possible to treat the atom-atom interactions in perturbation theory. Furthermore we assume temperatures which allow a semiclassical treatment of the cooling process. The effect of the presence of other atoms can be separated analytically into two parts; an attenuation force due to the absorption of the laser beams in the atomic cloud similar to the results of Dalibard [Opt. Commun. 68, 203 (1988)], which tends to compress the atomic cloud, and a two-atom force due to photon emission and absorption cycles between different atoms. This force proves to be repulsive for the configurations studied and prevents the cloud from collapsing. The result for the first-order perturbation expansion in collision strength generalizes the model proposed by Walker, Sesko, and Wieman [J. Opt. Soc. B 8, 946 (1991)] by including additional terms, such as those associated with Raman couplings.
©1994 The American Physical Society
- J. Lawall, M. Prentiss, L. S. Goldner, C. Gerz, S. L. Rolston, C. I. Westbrook, W. D. Phillips, P. Marte, P. Zoller, Pushing atoms with darkness, Adiabatic momentum transfer, Optics and Photonic News (1994-12-28), (ID: 375176)
- I. Marzoli, J. I. Cirac, R. Blatt, P. Zoller, Laser cooling of trapped three-level ions: Designing two-level systems for sideband cooling, Physical Review A 49, 2771–2779, (1994-04-04), URL doi:10.1103/PhysRevA.49.2771 (ID: 375175) Toggle Abstract
Laser cooling of three-level ions of the cascade, vee, and lambda configuration is considered with simultaneous excitation on a weak and strong transition. Choosing appropriate parameters for the Rabi frequencies and the respective detunings allows one to eliminate adiabatically one of the levels. The thus designed two-level ion can acquire decay rates Γ’ smaller than the trap frequency ν such that sideband cooling becomes possible and accordingly allows cooling of the ion to its lowest oscillator state 〈n〉=0 in the trap. Explicit expressions for the detunings and the Rabi frequencies for sideband cooling of the effective two-level system are derived.
©1994 The American Physical Society
- P. Marte, R. Dumhart, R. Taïeb, P. Zoller, M. S. Shahriar, M. Prentiss, Polarization-gradient-assisted subrecoil cooling: Quantum calculations in one dimension, Physical Review A 49, 4826–4836, (1994-06-06), URL doi:10.1103/PhysRevA.49.4826 (ID: 375174) Toggle Abstract
We present a fully quantum-mechanical analysis of laser cooling of an angular momentum Jg=1 to Je=1 transition in a laser configuration consisting of two counterpropagating linearly polarized laser beams. The essential feature of this configuration is the coexistence of velocity-selective coherent population trapping (VSCPT) and polarization-gradient cooling. The role of polarization-gradient cooling is to provide (i) for short interaction times ‘‘precooling’’ of the initial momentum distribution and (ii) in the long-time limit ‘‘confinement of velocities.’’ This eventually leads to a larger number of atoms being captured in the dark state when compared with the schme of Aspect et al. [Phys. Rev. Lett. 61, 826 (1988)]. We find that the optimum parameter values for polarization-gradient cooling and VSCPT are in a completely different parameter regime: polarization-gradient cooling works best off resonance and for low intensities, while VSCPT works best on resonance. We can combine the advantages of polarization-gradient cooling and VSCPT in a scheme where we cycle in time between the optimum cooling parameters for both cooling mechanisms.
©1994 The American Physical Society
- S. Marksteiner, C. M. Savage, P. Zoller, S. L. Rolston, Coherent atomic waveguides from hollow optical fibers: Quantized atomic motion, Physical Review A 50, 2680–2690, (1994-09-03), URL doi:10.1103/PhysRevA.50.2680 (ID: 375173) Toggle Abstract
We present a theoretical analysis of coherent atomic motion through a straight atomic waveguide constructed from a hollow optical fiber. Atoms are guided by the evanescent light field at the fiber’s interior glass-vacuum interface. The atoms’ internal structure is modeled by a Jg=0 to Je=1 transition. The atomic wave functions are determined and the loss rates due to spontaneous emission, tunneling to the wall, and nonadiabatic transitions are estimated. The influence of Casimir-Polder forces is considered. We conclude with a discussion of the feasibility of the proposed waveguides.
©1994 The American Physical Society
- R. Taïeb, R. Dumhart, J. I. Cirac, P. Marte, P. Zoller, Cooling and localization of atoms in laser-induced potential wells, Physical Review A 49, 4876–4887, (1994-06-06), URL doi:10.1103/PhysRevA.49.4876 (ID: 375172) Toggle Abstract
We discuss theoretically the cooling and localization of atoms in deep potentials induced by a far-off-resonant standing-wave laser. For a two-level atom cooling occurs via a Sisyphus mechanism. For a Λ system we discuss a Raman cooling scheme similar to the one proposed for laser cooling in ion traps.
©1994 The American Physical Society
- R. Walser, P. Zoller, Laser-noise-induced polarization fluctuations as a spectroscopic tool, Phys. Rev. A 49, 5067–5077, (1994-06-06), URL doi:10.1103/PhysRevA.49.5067 (ID: 375170) Toggle Abstract
We have investigated theoretically the possibility of employing noisy laser fields for spectroscopic purposes. The basis for this spectroscopy is a modification of the statistic of the fluctuations caused by the nonlinear interaction. All atomic resonances within the range of several bandwidths can be observed in the power spectrum, even in case of large inhomogeneous broadening. We have derived analytical, nonperturbative results for a real Gaussian, a complex Gaussian, and a phase-diffusing field. The mean transmitted intensity and its variance as well as the power spectrum have been evaluated in the limit of weak absorption for two-level systems. Without modification, we can apply our results also to other transition schemes. As an example, the power spectrum of the D2 transition of 133Cs driven by a phase-diffusing field is calculated. For this four-level system we find qualitative agreement with experimental results by Yabuzaki et al. [Phys. Rev. Lett. 67, 2453 (1991)].
- R. Walser, J. Cooper, P. Zoller, Saturated absorption spectroscopy using diode-laser phase noise, Physics Letters A 50, 4303–4309, (1994-11-05), URL doi:10.1103/PhysRevA.50.4303 (ID: 375171) Toggle Abstract
We have investigated theoretically the applicability of phase-fluctuating laser fields in saturated absorption spectroscopy. The fluctuations of pump and probe fields are fully correlated if they are derived from the same laser source. Inside the saturable medium, phase fluctuations are converted into intensity noise. This nonlinear mixing modifies the statistics of the transmitted fields. By measuring higher-order correlations one can deduce additional spectroscopic information. Apart from the mean intensity, we have examined the intensity noise and intensity power spectrum of the weak probe field. The resonances of these correlation functions are also unaffected by large inhomogeneous broadening since they are inherently related to the usual saturated absorption dip. We find qualitative agreement with results of a recent experiment employing this technique [D. H. McIntyre et al., Opt. Lett. 18, 1816 (1993)], which demonstrates the advantages of noise spectroscopy using spectrum analyzers.
- J. I. Cirac, R. Blatt, A. S. Parkins, P. Zoller, Quantum collapse and revival in the motion of a single trapped ion, Phys. Rev. A 49, 1202–1207, (1994-02-02), URL doi:10.1103/PhysRevA.49.1202 (ID: 375187) Toggle Abstract
Within certain limits, the dynamics of a single trapped ion oscillating about the node of a standing-wave light field is described by the Jaynes-Cummings model, which is routinely used for cavity-QED experiments. We propose a technique to measure quantum collapse and revival in the population inversion of a single trapped ion, and show that this method is uniquely suited for the measurement of final temperatures of the trapped ion as well as for the analysis of nonclassical states of the ion motion, such as Fock and squeezed states. The results are discussed with particular consideration given to the effects of a finite laser bandwidth.
©1994 The American Physical Society
- J. I. Cirac, L. J. Garay, R. Blatt, A. S. Parkins, P. Zoller, Laser cooling of trapped ions: The influence of micromotion, Phys. Rev. A 49, 421–432, (1994-01-01), URL doi:10.1103/PhysRevA.49.421 (ID: 375185) Toggle Abstract
Laser cooling of a single trapped ion in a Paul trap is discussed theoretically in the Lamb-Dicke limit, with full consideration of the time dependence of the trapping potential. Resulting mean kinetic energies are defined as time averages over one period of the micromotion and are compared with final temperatures expected from the laser-cooling treatment with harmonic traps. For laser-atom detunings close to the micromotion frequency the results differ significantly from those expected for a harmonic trap potential. A physical interpretation is given and simple formulas are derived for the strong confinement case.
©1994 The American Physical Society
- J. I. Cirac, R. Blatt, P. Zoller, Nonclassical states of motion in a three-dimensional ion trap by adiabatic passage, Phys. Rev. A 49, R3174–R3177, (1994-05-05), URL doi:10.1103/PhysRevA.49.R3174 (ID: 375186) Toggle Abstract
A scheme for the preparation of nonclassical states of motion in a three-dimensional harmonic ion trap is proposed. The technique is based on adiabatic passage along dressed energy levels of the strongly coupled ion-trap system by varying the laser frequency.
©1994 The American Physical Society
- M. Lewenstein, J. I. Cirac, P. Zoller, Quantum dynamics of a laser-cooled ideal gas, Phys. Rev. A 50, 3409–3422, (1994), URL doi:10.1103/PhysRevA.50.3409 (ID: 305615) Toggle Abstract
We study a system of bosonic or fermionic atoms in a microscopic trap undergoing laser cooling. We derive a master equation governing the evolution of such a system, and show that the stationary state can be described by Bose-Einstein or Fermi-Dirac distributions. The quantum-statistical character of the atoms exhibits itself in the dynamical behavior of the system and in the statistical properties of fluorescence photons emitted in the stationary state.
- J. I. Cirac, P. Zoller, Laser cooling of trapped ions in a squeezed vacuum, Phys. Rev. A 47, 2191–2195, (1993-03-03), URL doi:10.1103/PhysRevA.47.2191 (ID: 375417) Toggle Abstract
Laser cooling a trapped ion damped by an electromagnetic reservoir in a squeezed-vacuum state is investigated. The cooling rate and the final temperature are given for the case in which the ion is located at the node of a laser standing wave, on resonance with its internal transition. In particular, we find that the ion can have final temperatures below the Dopper limit.
©1993 The American Physical Society
- P. Marte, R. Dumhart, R. Taïeb, P. D. Lett, P. Zoller, Quantum wave function simulation of the resonance fluorescence spectrum from one-dimensional optical molasses, Phys. Rev. Lett. 71, 1335–1338, (1993-08-09), URL doi:10.1103/PhysRevLett.71.1335 (ID: 375416) Toggle Abstract
Using recently developed quantum wave function techniques, we have performed a simulation of 85Rb atoms in a one-dimensional optical molasses, formed from counterpropagating laser beams with orthogonal linear polarizations. Both internal and external degrees of freedom are treated quantum mechanically in one dimension and the spectrum of resonance fluorescence is calculated and compared to recent experiments. Excellent agreement is obtained for the spectrum and additional insight is gained into the experimental evidence for quantized motion in the optical potentials.
©1993 The American Physical Society
- P. Marte, R. Dumhart, R. Taïeb, P. Zoller, Resonance fluorescence from quantized one-dimensional molasses, Phys. Rev. A 47, 1378–1390, (1993-02-02), URL doi:10.1103/PhysRevA.47.1378 (ID: 375414) Toggle Abstract
We study theoretically the spectrum of resonance fluoresence from one-dimensional molasses consisting of two-level atoms with Zeeman substructure. The center-of-mass motion of the atom is treated fully quantum mechanically. The spectrum shows sidebands due to transitions between vibrational levels in optical potentials generated by the laser light. Detailed results are presented for the Jg=1/2→Je=3/2 atomic transition in a laser configuration with two counterpropagating waves with orthogonal polarizations. We have solved the corresponding quantum master equation and calculated the relevant autocorrelation function of the atomic dipole using (i) a direct numerical solution of the master equation, (ii) a wave-function simulation of the master equation and correlation function employing periodic time-dependent Bloch wave functions, and (iii) a semiclassical bipotential calculation for the spectrum including a simple quantum correction.
©1993 The American Physical Society
- A. S. Parkins, P. Marte, P. Zoller, H. J. Kimble, Synthesis of arbitrary quantum states via adiabatic transfer of Zeeman coherence, Phys. Rev. Lett. 71, 3095–3098, (1993-11-08), URL doi:10.1103/PhysRevLett.71.3095 (ID: 375413) Toggle Abstract
A scheme for the preparation of general coherent superpositions of photon-number states is proposed. By strongly coupling an atom to a cavity field, atomic ground-state Zeeman coherence can be transferred by (coherent) adiabatic passage to the cavity mode and a general field state can be generated without atomic projection noise.
©1993 The American Physical Society
- A. S. Parkins, P. Zoller, H. J. Carmichael, Spectral linewidth narrowing in a strongly coupled atom-cavity system via squeezed-light excitation of a ‘‘vacuum’’ Rabi resonance, Phys. Rev. A 48, 758–763, (1993-01-07), URL doi:10.1103/PhysRevA.48.758 (ID: 375410) Toggle Abstract
The system consisting of a two-level atom coupled strongly to a cavity mode behaves as a two-state system when excited near one of the ‘‘vacuum’’ Rabi resonances. With finite-bandwidth squeezed light incident upon the cavity and tuned to one of these resonances, we show that it is possible to realize a two-state system coupled to a squeezed vacuum. This system exhibits subnatural linewidths in the emitted spectra, as described by Gardiner [Phys. Rev. Lett. 56, 1917 (1986)] in a study of spontaneous emission of a two-level atom in a squeezed vacuum, but requires that only a single cavity mode be subject to squeezing rather than the entire three-dimensional vacuum.
©1993 The American Physical Society
- R. Taïeb, P. Marte, R. Dumhart, P. Zoller, Spectrum of resonance fluorescence and cooling dynamics in quantized one-dimensional molasses: Effects of laser configuration, Phys. Rev. A 47, 4986–4993, (1993-06-06), URL doi:10.1103/PhysRevA.47.4986 (ID: 375409) Toggle Abstract
We study theoretically the spectrum of resonance fluorescence and laser-cooling dynamics corresponding to quantized atomic motion in one-dimensional optical molasses. We consider an atom with a Jg=1→Je=2 transition interacting with two counterpropagating laser beams. The laser light is assumed to be linearly polarized with an angle θ between the polarization vectors. We discuss the spectrum of resonance fluorescence, the spectroscopy of band structure in the optical potentials, and the population of the vibrational quantum levels as a function of the angle between the polarization vectors.
©1993 The American Physical Society
- H. R. Xia, J. I. Cirac, S. Swartz, B. Kohler, D. Elliott, J. Hall, P. Zoller, Phase shifts and intensity dependence in frequency-modulation spectroscopy, JOSA B 11, 721, (1993-06-06), URL (ID: 375387) Toggle Abstract
Phase shifts and intensity dependence in frequency-modulation spectroscopy
- J. I. Cirac, A. S. Parkins, R. Blatt, P. Zoller, Cooling of a trapped ion coupled strongly to a quantized cavity mode, Optics Communications 97, 353-359, (1993-04-01), URL doi:10.1016/0030-4018(93)90502-V (ID: 375419) Toggle Abstract
The interaction of a trapped two-level ion, confined in a harmonic potential, with a quantized cavity mode of the radiation field is studied theoretically. The ion is considered to be spatially localized on the scale of the optical wavelength (Lamb-Dicke limit), and the ion-cavity-mode coupling is assumed to be larger than or comparable to the spontaneous emission and cavity-mode loss rates. With broadband thermal light driving the cavity mode, we show that the cooling rates and final temperatures of the trapped-ion motion reflect the Jaynes-Cummings energy spectrum of the strongly-coupled ion-cavity system.
1 Present address: Departamento de Fisica Aplicada, Facultad de Ciencias, Paseo Universidad 4, 13071 Ciudad Real, Spain.
2 Permanent address: I. Institut für Laserphysik, Jungiusstr. 9, W-2000 Hamburg 36, Germany.
- J. I. Cirac, R. Blatt, A. S. Parkins, P. Zoller, Spectrum of resonance fluorescence from a single trapped ion, Phys. Rev. A 48, 2169–2181, (1993-09-03), URL doi:10.1103/PhysRevA.48.2169 (ID: 375421) Toggle Abstract
The spectrum of resonance fluorescence of a single trapped and laser-cooled ion is studied theoretically. The quantum motion of the trapped particle manifests itself in the form of narrow motional sidebands in the fluorescence spectrum. For our calculations it is assumed that the ion is confined to dimensions much smaller than the optical wavelength (Lamb-Dicke limit) and the approach is valid for multilevel systems, general trapping potentials, and for both traveling-wave and standing-wave configurations. The motional sidebands in the spectrum have asymmetric amplitudes and this asymmetry is shown to depend on the ion energy, the detector position, and the choice of standing- or traveling-wave laser excitation.
©1993 The American Physical Society
- J. I. Cirac, R. Blatt, A. S. Parkins, P. Zoller, Laser cooling of trapped ions with polarization gradients, Phys. Rev. A 48, 1434–1445, (1993-08-02), URL doi:10.1103/PhysRevA.48.1434 (ID: 375420) Toggle Abstract
Laser cooling of a single trapped ion with Zeeman substructure below the Doppler limit is considered theoretically. The laser field consists of two counterpropagating beams linearly polarized in different directions, and the internal atomic transition is Jg=1/2→Je=3/2. The ion is assumed to be localized to spatial dimensions smaller than the optical wavelength (Lamb-Dicke limit) and placed at a specific position with respect to the laser beams. Under the assumption that the rate for optical pumping between the atomic ground states defines the smallest time constant in the system, analytic expressions for the final energy and the cooling rates are derived, with both a semiclassical and a full quantum treatment. The results show that laser cooling of a trapped ion using polarization gradients leads to very low energies. These energies are insensitive to the precise localization of the ion with respect to the lasers, the angle between the direction of the polarizations of the laser beams, and the detuning of the cooling laser.
©1993 The American Physical Society
- J. I. Cirac, A. S. Parkins, R. Blatt, P. Zoller, ‘‘Dark’’ squeezed states of the motion of a trapped ion, Phys. Rev. Lett. 70, 556–559, (1993-02-01), URL doi:10.1103/PhysRevLett.70.556 (ID: 375418) Toggle Abstract
We propose a scheme for preparing coherent squeezed states of motion in an ion trap based on the multichromatic excitation of a trapped ion by standing- and traveling-wave light fields. The squeezed state is produced when the beat frequency between two standing-wave light fields is equal to twice the trap frequency, and is indicated by a ‘‘dark resonance’’ in the fluorescence emitted by the ion.
©1993 The American Physical Society
- J. I. Cirac, R. Blatt, A. S. Parkins, P. Zoller, Preparation of Fock states by observation of quantum jumps in an ion trap, Phys. Rev. Lett. 70, 762–765, (1993-02-06), URL doi:10.1103/PhysRevLett.70.762 (ID: 375422) Toggle Abstract
We propose a technique for the preparation of Fock states of a harmonic oscillator strongly coupled to a single two-level atomic transition based on the observation of quantum jumps. Examples are taken from the fields of cavity QED and ion trapping, where photon number states and number states of the quantized atomic motion may be prepared, respectively.
©1993 The American Physical Society
- M. H. Anderson, G. Vemuri, J. Cooper, P. Zoller, S. Smith, Experimental study of absorption and gain by two-level atoms in a time-delayed non-Markovian optical field, Phys. Rev. A 47, 3202–3209, (1993-04-04), URL doi:10.1103/PhysRevA.47.3202 (ID: 375423) Toggle Abstract
We have measured the absorption from a weak time-delayed probe field by a two-level atomic system [Na 3s1/2(F=2,mF=2)→3p3/2(F=3,mF=3)] saturated by a phase-diffusing pump field. The pump and probe, derived from the same artificially-noise-modulated phase-diffusing laser beam, are frequency degenerate and resonant with the atomic transition. The probe is a time-delayed replica of the pump. Our results, carried out in a regime where the field bandwidth and the Rabi frequency are comparable, provide confirmation of recent theoretical predictions [K. Gheri, M. A. M. Marte, and P. Zoller, J. Opt. Soc. Am. B 5, 1559 (1991)] for the atomic response to the non-Markovian composite of a pump and time-delayed probe, valid for arbitrary bandwidths and intensities. Amplification of the probe field is observed for delays comparable to the lifetime of the upper level and again for very long delays, if the bandwidth is less than the decay rate of the upper state.
©1993 The American Physical Society
- A. S. Parkins, P. Zoller, σ+-σ- laser-cooling configuration with broadband laser fields: Instability at zero velocity, Phys. Rev. A 45, R6161–R6164, (1992-05-01), URL doi:10.1103/PhysRevA.45.R6161 (ID: 375596) Toggle Abstract
We investigate theoretically laser cooling with broadband σ+-σ- lasers acting on J=0→J=1 and J=1→J=2 transitions. For cross-correlated laser fluctuations an instability in the friction force at zero velocity is predicted for red laser detunings. The dependence of this instability on the cross-correlation and spectral line shape is investigated.
©1992 The American Physical Society
- A. S. Parkins, P. Zoller, Laser cooling of atoms with broadband real Gaussian laser fields, Phys. Rev. A 45, 6522–6538, (1992-05-01), URL doi:10.1103/PhysRevA.45.6522 (ID: 375592) Toggle Abstract
We describe a theoretical approach to laser cooling with broadband real Gaussian laser fields that is based on adiabatic elimination methods and the Fokker-Planck equation for the Wigner function. This approach is used to model the recent broadband cooling experiment of Zhu, Oates, and Hall [Phys. Rev. Lett. 67, 46 (1991)] and gives correct order-of-magnitude results. The theory is then applied to J=0→J=1 and J=1→J=2 transitions in a σ+-σ- optical molasses configuration with correlated broadband laser fields. An instability in the cooling scheme at zero velocity is found for red laser detunings, and sub-Doppler-width velocity distributions are predicted for J=1→J=2 transitions with both red and blue laser detunings.
©1992 The American Physical Society
- H. Ritsch, P. Zoller, Quantum noise reduction in Raman lasers, Europhys. Lett. 19, 7, (1992), (ID: 375591) Toggle Abstract
Quantum noise reduction in Raman lasers
- H. Ritsch, P. Zoller, Dynamic quantum-noise reduction in multilevel-laser systems, Phys. Rev. A 45, 1881–1892, (1992-02-01), URL doi:10.1103/PhysRevA.45.1881 (ID: 375590) Toggle Abstract
Based on the standard laser model of a large number N of model atoms resonantly coupled to a single lasing mode, we show that the nonlinear dynamics of the active atoms of the laser can lead to output-intensity fluctuations significantly reduced below the shot-noise level. We identify the multiple recycling of the active electron from the lower lasing level to the upper level through the pumping as the key process leading to this dynamic-pump-noise reduction. This process has been neglected in most of the standard treatments of the laser so far. We find that the results are closely related to recent calculations based on the assumption of an external regular pump. For the widely used four-level model of the active atoms, the intensity noise can be reduced 50% below the shot-noise level. Generalizing the model to an m-level system, we find a quantum-noise reduction by a factor of 1/2m/(m-1)(m≥3), leading to perfect output-intensity noise reduction in the limit of a large number of intermediate steps in the recycling process of the active atoms. Finally, we demonstrate that the bandwidth of the noise reduction can be significantly enhanced using a nonlinear absorber in the cavity.
©1992 The American Physical Society
- R. Walser, H. Ritsch, P. Zoller, J. Cooper, Laser-noise-induced population fluctuations in two-level systems: Complex and real Gaussian driving fields, Phys. Rev. A 45, 468–476, (1992-02-01), URL doi:10.1103/PhysRevA.45.468 (ID: 375428) Toggle Abstract
The nonlinear dynamics of a sample of two-level systems exposed to noisy laser light is investigated. As stochastic models we treat the chaotic field and the real Gaussian field. Based on the method of marginal characteristic functions, we deduce analytical solutions for the mean values and variances of the atomic populations in terms of matrix continued fractions. We find significantly enhanced on-resonance fluctuations for a real Gaussian field compared to a chaotic field of the same bandwidth and intensity. Furthermore, in contrast to phase-noise models, the fluctuations in the fluorescence intensity do not decrease to zero in the limit of slow fluctuations.
©1992 The American Physical Society
- R. Graham, D. Walls, P. Zoller, Emission from atoms in linear superpositions of center-of-mass wave packets, Phys. Rev. A 45, 5018–5030, (1992-04-01), URL doi:10.1103/PhysRevA.45.5018 (ID: 375865) Toggle Abstract
We study theoretically the electromagnetic field emitted by atoms prepared in linear superpositions of several internal states, each of which is attached to a different center-of-mass wave packet by the preparation process. It is shown that the motion and mutual separation of the wave packets can be monitored either by observing the coherent spontaneous emission in a heterodyne experiment or by measuring the energy-absorption rate from a weak probe-laser beam. We also show that a three-level system involving three wave packets coherently emits photons, forming a linear superposition of states of opposite wave vectors. A heterodyne scheme for detecting the photons in this state is proposed.
©1992 The American Physical Society
- R. Graham, M. Schlautmann, P. Zoller, Dynamical localization of atomic-beam deflection by a modulated standing light wave, Mod. Phys. Lett. A 45, R19–R22, (1992-01-01), URL doi:10.1103/PhysRevA.45.R19 (ID: 375870) Toggle Abstract
The deflection of an atomic beam passing a standing-wave laser field in front of an oscillating mirror occurs by chaotic diffusive momentum transfer in a classical description and, as we show, is limited by dynamical localization quantum mechanically. An experiment to observe this quantum effect in an atomic beam is proposed.
©1992 The American Physical Society
- M. Marte, P. Zoller, Localization of atoms in light fields: Optical molasses, adiabatic compression and squeezing, Appl. Phys. B 54/5, 477 - 485, (1992-05-01), URL doi:10.1007/BF00325394 (ID: 375719) Toggle Abstract
It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.
- R. Dumhart, A. S. Parkins, P. Zoller, Gardiner, Crispin, Monte Carlo simulation of master equations in quantum optics for vacuum, thermal, and squeezed reservoirs, Phys. Rev. A 46, 4382–4396, (1992-10-01), URL doi:10.1103/PhysRevA.46.4382 (ID: 375893) Toggle Abstract
Wave-function simulation of the master equation in terms of quantum jumps is illustrated for vacuum, thermal, and squeezed reservoirs. We discuss simulation techniques for (i) atomic density matrices, and resonance fluoresence and weak-field absorption spectra of atoms, (ii) decay of a two-level system in a squeezed vacuum, and (iii) a strongly coupled atom-cavity system driven by thermal light.
©1992 The American Physical Society
- R. Dumhart, P. Zoller, H. Ritsch, Monte Carlo simulation of the atomic master equation for spontaneous emission, Phys. Rev. A 45, 4879–4887, (1992-04-01), URL doi:10.1103/PhysRevA.45.4879 (ID: 375891) Toggle Abstract
A Monte Carlo simulation of the atomic master equation for spontaneous emission in terms of atomic wave functions is developed. Realizations of the time evolution of atomic wave functions are constructed that correspond to an ensemble of atoms driven by laser light undergoing a sequence of spontaneous emissions. The atomic decay times are drawn according to the photon count distribution of the driven atom. Each quantum jump of the atomic electron projects the atomic wave function to the ground state of the atom. Our theory is based on a stochastic interpretation and generalization of Mollow’s pure-state analysis of resonant light scattering, and the Srinivas-Davies theory of continuous measurements in photodetection. An extension of the theory to include mechanical light effects and a generalization to atomic systems with Zeeman substructure are given. We illustrate the method by simulating the solutions of the optical Bloch equations for two-level systems, and laser cooling of a two-level atom in an ion trap where the center-of-mass motion of the atom is described quantum mechanically.
©1992 The American Physical Society
- Gardiner, Crispin, A. S. Parkins, P. Zoller, Wave-function quantum stochastic differential equations and quantum-jump simulation methods, Phys. Rev. A 46, 4363–4381, (1992-10-01), URL doi:10.1103/PhysRevA.46.4363 (ID: 375890) Toggle Abstract
The quantum-stochastic-differential-equation formulation of driven quantum-optical systems is carried out in the interaction picture, and quantum stochastic differential equations for wave functions are derived on the basis of physical principles. The Ito form is shown to be the most practical, since it already contains all the radiation reaction terms. The connection between this formulation and the master equation is shown to be very straightforward. In particular, a direct connection is made to the theory of continuous measurements, which leads directly to the method of quantum-jump simulations of solutions of the master equation. It is also shown that all conceivable spectral and correlation-function information in output fields is accessible by means of an augmentation of the simulation process. Finally, the question of the reality of the jumps used in the simulations is posed.
©1992 The American Physical Society
- J. I. Cirac, R. Blatt, P. Zoller, W. D. Phillips, Laser cooling of trapped ions in a standing wave, Phys. Rev. A 46, 2668–2681, (1992-09-01), URL doi:10.1103/PhysRevA.46.2668 (ID: 375895) Toggle Abstract
Laser cooling of trapped ions in a standing- and running-wave configuration is discussed theoretically. The ions are assumed to be spatially localized on the scale provided by the wavelength of the laser (Lamb-Dicke limit). A master equation for the center-of-mass distribution of the ion is derived for a multilevel system, and explicit results are presented for two- and three-level systems and harmonic trapping potentials. For the two-level system located at the node of the standing wave, we find final temperatures that are a factor of 2 lower than the limit for a running wave and cooling rates that do not saturate with the laser intensity. At the point of maximum gradient of the standing wave, blue detuned cooling is found that is analogous to the Sisyphus cooling of free atoms. For a three-level system we compare our results with those of Wineland, Dalibard, and Cohen-Tannoudji [J. Opt. Soc. Am. B 9, 32 (1992)].
©1992 The American Physical Society
- G. Alber, P. Zoller, Laser induced excitation of electronic Rydberg wave packets, Contemporary physics 32, 185, (1991), (ID: 376525) Toggle Abstract
Laser induced excitation of electronic Rydberg wave packets
- K. Ellinger, H. Gratl, P. Zoller, New aspects in laser excitation of Rydberg wavepackets, Physica Scripta T34, 60, (1991), (ID: 376491) Toggle Abstract
New aspects in laser excitation of Rydberg wavepackets
- G. Alber, P. Zoller, Laser excitation of electronic wave packets in rydberg atoms, Physics Reports 199(5), 231-280, (1991-01-05), URL doi:10.1016/0370-1573(91)90058-T (ID: 376488) Toggle Abstract
We review recent theoretical and experimental work on laser-induced excitation of atomic Rydberg wave packets. Studying the motion of these wave packets provides a bridge between quantum mechanics and the classical concept of the trajectory of an electron and corresponds to real-time observations of atomic dynamics in a Coulomb, and possibly static external field. We discuss generation and detection of wave packets by short and/or intense laser pulses. On the theoretical side our emphasis is on quantum defect theory and semiclassical methods.
- J. I. Cirac, H. Ritsch, P. Zoller, Two-level system interacting with a finite-bandwidth thermal cavity mode, Phys. Rev. A 44, 4541–4551, (1991-10-01), URL doi:10.1103/PhysRevA.44.4541 (ID: 376271) Toggle Abstract
The interaction of a two-level system with a single quantized mode of the radiation field of finite bandwidth in a thermal state and coupled to background vacuum modes is considered theoretically. A hierarchy of equations for atom-field moments is derived and solved in terms of continued fractions. The population inversion, the spectrum of resonance fluorescence, and the photon statistics of the cavity mode are calculated.
©1991 The American Physical Society
- P. Marte, P. Zoller, Hydrogen in intense laser fields: Radiative close-coupling equations and quantum-defect parametrization, Phys. Rev. A 43, 1512–1522, (1991-02-01), URL doi:10.1103/PhysRevA.43.1512 (ID: 376269) Toggle Abstract
A system of radiative close-coupling equations for a hydrogen atom in a circularly polarized intense laser field is derived. The radiative scattering matrix is parametrized within a multichannel quantum-defect formalism. The quasienergy spectrum corresponding to nonperturbative shifts and ionization widths of the bound atomic states is computed from the poles of the radiative scattering matrix. For an intensity range up to α0≊1.5a0 (with α0 the oscillation amplitude of the free electron in the laser and a0 the Bohr radius), numerical results are presented in the frequency regime where two-photon ionization and above-threshold ionization of the ground state is possible. For one-photon transitions a stabilization of the atomic states for strong fields is predicted.
©1991 The American Physical Society
- H. Ritsch, P. Zoller, Gardiner, Crispin, D. Walls, Sub-Poissonian laser light by dynamic pump-noise suppression, Physical Review A 44, 3361–3364, (1991-09-01), URL doi:10.1103/PhysRevA.44.3361 (ID: 376267) Toggle Abstract
We identify a mechanism of dynamical pump-noise suppression in lasers. It is based on the recycling of the active laser electron from the lower to the upper laser level by a sequence of incoherent step processes. Although each of these steps corresponds to a Poisson process, i.e., is stochastic, the combination of many incoherent steps leads to a regular (deterministic) recycling of the laser electron and, correspondingly, a pump-noise suppression in the laser. The mechanism predicts sub-Poissonian laser output and intensity fluctuations beyond the shot-noise limit for incoherently pumped systems.
©1991 The American Physical Society
- P. Marte, P. Zoller, J. Hall, Coherent atomic mirrors and beam splitters by adiabatic passage in multilevel systems, Phys. Rev. A 44, R4118–R4121, (1991-10-01), URL doi:10.1103/PhysRevA.44.R4118 (ID: 376268) Toggle Abstract
We study atomic-beam deflection by adiabatic passage between Zeeman ground levels via Raman transitions induced by counterpropagating σ±-polarized lasers. We show that complete population transfer between the ground states can be achieved, which corresponds to the scattering of the atomic wave packet into a single final momentum state by absorption and induced emission of laser photons. Although the lasers can be resonant, the excited state(s) are never populated during the adiabatic transfer, which suppresses the effects of spontaneous emission and preserves the coherence of the atomic wave function. This scheme has attractive features as a beam splitter and mirror for atomic interferometry.
©1991 The American Physical Society
- M. Marte, J. I. Cirac, P. Zoller, Deflection of Atoms by Circularly Polarized Light Beams in Triple Laue Configuration, J. Mod. Opt. 38/11, 2265 - 2280, (1991-11-11), URL (ID: 376278) Toggle Abstract
A new type of atomic interferometer is discussed, in which atoms with two ground-state Zeeman sub-levels m = - 1 , and an excited state with m = 0 , pass through three laser interaction zones-each comprising two counter-propagating waves of opposite circular polarization with a large detuning from resonance. By means of Raman-type transitions between the two ground-state levels, which convey a recoil of two photon momenta, the atomic wave function is split up into two coherent spatially separated branches, and subsequently recombined. In this system, conservation of energy and momentum leads to a strong correlation between the external centre of mass motion and internal magnetic degrees of freedom. As a consequence, the paths within the interferometer are tagged by the internal quantum number m . As an example, we calculate the position and momentum distribution function of a helium atom on its way through the interferometer.
- K. M. Gheri, M. Marte, P. Zoller, Atomic absorption in cross-correlated time-delayed stochastic laser fields, JOSA B 8, 1559, (1991), URL (ID: 376281) Toggle Abstract
Atomic absorption in cross-correlated time-delayed stochastic laser fields
- A. Giusti-Suzor, P. Zoller, Rydberg electrons in laser fields: A finite-range-interaction problem, Phys. Rev. A 36, 5178–5188, (1987-12-01), URL doi:10.1103/PhysRevA.36.5178 (ID: 376903) Toggle Abstract
A theory of Rydberg and continuum states in intense laser fields is developed based on the observation that the effect of laser radiation can be described in a scattering formulation as a finite-volume interaction coupling Coulomb-type fragmentation channels. In particular, laser-induced couplings may be incorporated in a multichannel quantum-defect treatment, in which a set of dressed channels corresponding to different photon numbers is defined, with intensity-dependent quantum defects and mixing angles. These quantities may be obtained by solving a system of close-coupling equations for the electron wave function, in a frame where the asymptotic electron oscillations are transformed away. This allows us to read off at a finite distance a radiative reaction matrix, which is a smooth function of energy for an energy range small compared with the photon frequency, and contains the net effect of radiative couplings. Calculations are presented for ionization of hydrogen s states in circularly polarized laser light, with allowance for above-threshold photon absorption.
©1987 The American Physical Society
- M. Hamilton, K. Arnett, S. Smith, D. Elliott, M. Dziemballa, P. Zoller, Saturation of an optical transition by a phase-diffusing laser field, Phys. Rev. A 36, 178–188, (1987-07-01), URL doi:10.1103/PhysRevA.36.178 (ID: 376901) Toggle Abstract
The dependence of the optical Autler-Townes effect on laser field phase fluctuations describable by a two-dimensional Markovian process (phase-diffusion model with a non-Lorentzian line shape) is investigated experimentally in atomic sodium. An intense cw laser tuned to near resonance with the 3S1/2(F=2,MF=2)→3P3/2(F=3,MF=3) transition was frequency modulated to generate phase fluctuations with the desired characteristics. A weak probe laser coupling to the 4D5/2(F=4, MF=4) state was used to obtain the double-peaked optical Autler-Townes absorption profiles in order to investigate their dependencies on band shape, bandwidth, intensity, and detuning of the intense fluctuating laser field. Reversals of the peak-height asymmetry and reversion to normal asymmetry with increased detuning were observed and measured. Quantitative studies of the spectral widths and splittings of the peaks are also reported. Measured absorption profiles are in excellent agreement with calculations based on previous theoretical work.
©1987 The American Physical Society
- W. Henle, H. Ritsch, P. Zoller, Rydberg wave packets in many-electron atoms excited by short laser pulses, Physical Review A 36, 683–692, (1987-07-02), URL doi:10.1103/PhysRevA.36.683 (ID: 376900) Toggle Abstract
An atomic electron excited to a coherent superposition of Rydberg states by a short laser pulse corresponds to a wave packet moving on a radial Kepler orbit. The dynamics of the motion of the wave packet can be observed in a two-photon process where a first laser pulse excites the wave packet, which at a later time is probed by a second pulse. In a many-electron atom a single valence electron excited to the Rydberg wave packet can exchange energy with the atomic ion core (electron correlation), whenever the Rydberg wave packet passes through the atomic core region. We can view this orbiting of the wave packet as a succession of below-threshold inelastic scattering events from the atomic ion core. A theory of two-photon absorption with time-delayed short laser pulses is developed which is based on a ‘‘smooth’’ multichannel quantum-defect Green function.
©1987 The American Physical Society
- W. Henle, P. Zoller, Multichannel quantum defect parametrisation of resonant multiphoton ionisation, Journal of Physics B; Atom. and Mol. Phy. 20, 4007-4025, (1987), URL doi:10.1088/0022-3700/20/16/013 (ID: 376899) Toggle Abstract
A theory of resonant multiphoton ionisation with perturbed Rydberg series as intermediate states is developed which parametrises the atomic density matrix equations with the help of multichannel quantum defect theory. The authors apply the theory to stepwise three-photon ionisation of Ba near the 5d7d 1D2 state.
- P. Zoller, M. Marte, D. Walls, Quantum jumps in atomic systems, Phys. Rev. A 35, 198–207, (1987-01-01), URL doi:10.1103/PhysRevA.35.198 (ID: 376897) Toggle Abstract
We consider a three-level atomic system driven strongly on one transition and weakly on the other. The excited state on the weak transition is assumed to be metastable. We give an analysis of the fluorescence from the strong transition in terms of the elementary probability density p[0,t)(t1,t2,..., tn) which gives us the probability density that exactly n photons are emitted at times t1,t2,...,tn by the atom in the time interval [0,t). We show that p[0,t) essentially factorizes into products of conditional densities c̃(τ) that, given a photon is emitted at time zero, the next photon emission occurs at time τ. This enables a simulation of the individual photon emissions to be given which shows directly the existence of prolonged dark windows in the fluorescence corresponding to the shelving of the electron in the metastable state or ‘‘quantum jumps.’’
©1987 The American Physical Society
- G. Alber, P. Zoller, Harmonic generation and multiphoton ionization near an autoionizing resonance, Phys. Rev. A 27, 1373–1388, (1983-03-03), URL doi:10.1103/PhysRevA.27.1373 (ID: 377390) Toggle Abstract
We theoretically study intensity-saturation effects in resonant harmonic generation and multiphoton ionization. A first laser excites a two-photon resonance which is coupled by a second laser to an autoionizing state. Starting from an effective Hamiltonian for the three resonant atomic states, we derive a set of equations for the density matrix of the gaseous medium and the electromagnetic field within a semiclassical framework. We present and discuss analytical and numerical solutions of these equations which show a variety of line profiles depending critically on the intensities of the incident laser pulses.
©1982 The American Physical Society
- G. Alber, P. Zoller, Spin polarization by selective laser-induced interference, Phys. Rev. A 27, 1713–1716, (1983-03-03), URL doi:10.1103/PhysRevA.27.1713 (ID: 377380) Toggle Abstract
States behaving like autoionizing states can be selectively induced by laser radiation into one of the continuum spin channels in the photoionization of polarized excited alkaki atoms. As a result of destructive or constructive interference between the direct ionization channel and those introduced by the dressing laser radiation, the cross section of this specific spin component is completely suppressed or enhanced, while leaving the other spin channel unaffected. The q parameter which determines the line shape of the Fano-type resonance can be resonantly tuned as a function of the dressing laser frequency.
©1983 The American Physical Society
- M. Lewenstein, P. Zoller, J. Mostowski, Path integration method applied to (N-1)-resonant N-photon ionisation, J. Phys. B: At. Mol. Opt. Phys. 16, 563-568, (1983), URL doi:10.1088/0022-3700/16/4/010 (ID: 377379) Toggle Abstract
The authors investigate the problem (N-1) resonant N-photon ionisation of an atom driven by a stochastic field. The authors compare ionisation rates in the presence of a phase-diffusing laser field and light undergoing Gaussian amplitude fluctuations (chaotic field). In the case of the chaotic field the authors obtain exact results with the help of the functional integration method. They also present numerical results for the case of three-resonant four-photon ionisation.
- E. Matthias, P. Zoller, D. Elliott, N. Piltch, S. Smith, G. Leuchs, Influence of Configuration Mixing in Intermediate States on Resonant Multiphoton Ionization, Phys. Rev. Lett. 50, 1914–1917, (1983-06-23), URL doi:10.1103/PhysRevLett.50.1914 (ID: 377377) Toggle Abstract
Resonant three-photon ionization of Ba to a structureless continuum via 6snd Rydberg states was performed in the range 19<~n<~30. It is shown that state mixing in the Rydberg states strongly affects the photoion and photoelectron yields as well as the angular distributions of photoelectrons. The experimental results are explained on the basis of a three-channel quantum-defect theory for the perturbed Rydberg series.
©1983 The American Physical Society
- T. Poston, D. Walls, P. Zoller, Multiple Bifurcations in Coherent n-photon Processes, Journal of Modern Optics 29, 1691 - 1704, (1983), URL (ID: 377133) Toggle Abstract
We consider a new class of bifurcations that may arise in multiphoton processes inside a coherently driven optical cavity involving more than one mode of the radiation field. For a non-saturable, non-linear medium, a single bifurcation point exists where the symmetric solution bifurcates into a number of non-symmetric solutions. The nature of the bifurcation ranges from a simple pitchfork bifurcation, in the case of four-wave mixing, to more complicated phenomena in higher-order processes. A saturable non-linear medium exhibits similar behaviour for low-input intensities; however, as the input intensity is increased the medium saturates, and at a second bifurcation point the symmetric branch regains its stability. The presence of fluctuations assures the accessibility of the symmetric branch. Thus, for example, for a two-photon absorbing medium we have the possibility of optical tristability involving one symmetric solution and two non-symmetric solutions.
- P. Zoller, Stark shifts and resonant multiphoton ionisation in multimode laser fields, J. Phys. B: At. Mol. Opt. Phys. 15, 2911, (1983), doi:10.1088/0022-3700/15/17/023 (ID: 377128) Toggle Abstract
The author presents a theory of resonant multiphoton ionisation by multimode laser light. He investigates N photon resonant N+1 photon ionisation for a high order bound-bound transition with the resonance dominated by the Stark shift. Two aspects of the problem are considered. He studies the bandwidth dependence for the resonant ionisation probability, approximating the multimode laser light by a chaotic field. Secondly, he investigates the effects of finite mode numbers of the multimode laser. Finally, the theory is compared with the recent experimental results of Lompre et al (1981).
- P. Zoller, J. Cooper, Nonlinear noise fields and strongly driven atomic transitions, Phys. Rev. A 28, 2310–2317, (1983-10-04), URL (ID: 377127) Toggle Abstract
A theory of the interaction of an atom with an intense nonlinear (non-Gaussian) noise field is developed, with emphasis on the connection with the underlying physics of laser coherence. We point out the possibility of obtaining exact solutions for the stochastically averaged atomic density matrix in terms of (matrix) continued fractions for a large class of nonlinear noise fields by generalizing the techniques developed by Risken and co-workers to solve nonlinear Fokker-Planck equations. As an example we discuss the absorption sepctrum of an atom strongly driven by noisy phase-locked radiation.
©1983 The American Physical Society
- C. Parigger, P. Zoller, D. Walls, Effect of Stark shift on two photon optical tristability, Optics Communications 44, 213-218, (1983-01-01), URL doi:10.1016/0030-4018(83)90203-1 (ID: 377120) Toggle Abstract
The effect of Stark shifts on two photon two mode optical multistability is investigated. We find that realistic Stark shifts produce significant changes in the state equations and their stability. Self oscillations, period doubling and optical chaos may occur.
- C. Leubner, P. Zoller, Gauge invariant interpretation of multiphoton transition probabilities, J. Phys. B: At. Mol. Opt. Phys. 13, 3613-3617, (1980), URL doi:10.1088/0022-3700/13/18/013 (ID: 377686) Toggle Abstract
It is shown by an elementary discussion that the proper discrimination between the energy operator of the system in a specified gauge and the so-called unperturbed Hamiltonian, as recently emphasised by Yang (1976), resolves apparent difficulties with the gauge invariant interpretation of multiphoton transition probabilities in some of the current literature. In particular, conditions more general than those usually quoted are established, under which either of the interactions -qx.E and -qA.p/m gives the same transition probabilities with the same unperturbed wavefunctions.
- D. Walls, P. Zoller, A coherent nonlinear mechanism for optical bistability from three level atoms, Optics Communications 34, 260-264, (1980-08-01), URL doi:10.1016/0030-4018(80)90029-2 (ID: 377685) Toggle Abstract
A novel scheme for optical bistability in a coherently driven three level atomic system is proposed. The scheme utilizes the non absorption resonance which occurs due to a population trapping in a coherent superposition of the ground state sublevels. The resulting optical bistability occurs for a lower threshold power than for a two level system and is insensitive to Doppler and laser bandwidth effects.
- P. Zoller, P. Lambropoulos, Laser temporal coherence effects in two-photon resonant three-photon ionisation, Journal of Physics B; Atom. and Mol. Phy. 13, 69-83, (1980), URL doi:10.1088/0022-3700/13/1/015 (ID: 377472) Toggle Abstract
Presents a theoretical analysis of the effect of laser light statistics on two-photon resonant three-photon ionisation of sodium. The ionisation probability and the population of the atom in the resonant state are compared in the presence of an intensity stabilised laser with a diffusing phase (phase diffusion model) and light undergoing Gaussian amplitude fluctuations (chaotic field). In the limit of large bandwidth fields the resonant two-photon excitation is statistically decoupled from the following ionisation step. A decrease of the bandwidth results in a partial correlation between these two steps manifesting itself in an enhancement of the ionisation probability in the chaotic field. With increasing intensity and the onset of saturation of the bound-bound transition, the ionisation probability and resonant excited-state population in the chaotic field may become smaller than the one in the phase diffusing light. In the large-bandwidth limit the Stark shift in the chaotic field is enhanced, which has a pronounced effect on the effective power-law dependence of the ionisation probability.
- P. Zoller, Laser photon correlation effects in electron scattering, Journal of Physics B; Atom. and Mol. Phy. 13, L249-L252, (1980), URL (ID: 377471) Toggle Abstract
Photon correlation effects are investigated on account of the multimode structure of laser radiation in electron scattering in the presence of an intense laser field. Appreciable deviations from the Kroll-Watson formula (1973) are found.
- G. Alber, P. Zoller, Light statistical dependence of saturated two-photon transitions, J. Phys. B: At. Mol. Opt. Phys. 13, 4567-4576, (1980), URL doi:10.1088/0022-3700/13/23/014 (ID: 377690) Toggle Abstract
The light statistical dependence of stationary saturated two-photon transitions is discussed. While at low intensities, in comparison with light having a stable amplitude, Gaussian amplitude fluctuations of the exciting radiation are more effective in populating the excited resonant state, light with amplitude fluctuations is less effective in saturating a two-photon transition. The amplitude fluctuations are shown to wash out the resonance curves. While at low intensities the effective Stark shift (i.e. the maximum of the dispersion curve) is larger by a factor of three in light with Gaussian amplitude fluctuations compared with radiation of constant amplitude, this enhancement factor becomes intensity dependent with increasing intensity.
- S. N. Dixit, A. Georges, P. Lambropoulos, P. Zoller, Comments on the short-time behaviour of multiphoton ionisation, J. Phys. B: At. Mol. Opt. Phys. 13, L157-L158, (1980), URL doi:10.1088/0022-3700/13/5/007 (ID: 377689) Toggle Abstract
Some questions regarding the applicability of theoretical results (1977, 1978) for the short-time behaviour of the multiphoton ionisation to the experiments are discussed. It is argued that the relevant conditions could not have been satisfied in the experiments concerned.
- S. N. Dixit, P. Zoller, P. Lambropoulos, Non-Lorentzian laser line shapes and the reversed peak asymmetry in double optical resonance, Phys. Rev. A 21, 1289–1296, (1980-04-04), URL doi:10.1103/PhysRevA.21.1289 (ID: 377688) Toggle Abstract
The interaction of an atomic system with a laser having phase fluctuations is studied within the phase-diffusion model, with the finite correlation time of the time derivative of the phase taken into account. This finite correlation time introduces a line shape which is Lorentzian near the center and falls off faster than the Lorentzian at its wings. The authors apply this model to calculate the spectrum of double optical resonance for excitation by a laser having this non-Lorentzian line shape. It is observed that the reversed peak asymmetry reverts to normal far off resonance owing to the cutoff of the laser spectrum, in agreement with recent experiments. Numerical results are presented.
©1980 The American Physical Society