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W. Kirkby, T. Bland, F. Ferlaino, R. N. Bisset Spin rotons and supersolids in binary antidipolar condensates,
SciPost Phys. 6 84 (2023-12-04),
http://dx.doi.org/10.21468/SciPostPhysCore.6.4.084 doi:10.21468/SciPostPhysCore.6.4.084 (ID: 721119)
Toggle Abstract
We present a theoretical study of a mixture of antidipolar and nondipolar Bose-Einstein condensates confined to an infinite tube. The long-ranged inverted dipolar interactions result in a spin roton instability associated with an unmodulated-to-supersolid phase transition. We present a phase diagram including unmodulated miscible, supersolid, incoherent domain, and macroscopic domain phases. The low densities of the binary mixture do not require beyond-mean-field quantum fluctuation corrections for stabilization. Our survey ranges from the quasi-1D to the radial Thomas-Fermi (elongated 3D) regimes. We also present the dynamic formation of supersolids following a quench from the uniform miscible phase, which maintains phase coherence across the system.
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E. Poli, T. Bland, S. White, M. J. Mark, F. Ferlaino, S. Trabucco, M. Mannarelli Glitches in rotating supersolids,
PRL 131 223401 (2023-11-29),
http://dx.doi.org/10.1103/PhysRevLett.131.223401 doi:10.1103/PhysRevLett.131.223401 (ID: 721122)
Toggle Abstract
Glitches, spin-up events in neutron stars, are of prime interest as they reveal properties of nuclear matter at subnuclear densities. We numerically investigate the glitch mechanism using analogies between neutron stars and magnetic dipolar gases in the supersolid phase. In rotating neutron stars, glitches are believed to occur when many superfluid vortices unpin from the interior, transferring angular momentum to the stellar surface. In the supersolid analogy, we show that a glitch happens when vortices pinned in the low-density inter-droplet region abruptly unpin. These supersolid glitches show remarkable parallels with neutron star glitches: they are characterized by a rapid spin-up followed by a long post-glitch spin-down due to relaxation towards a steady state. Dipolar supersolids offer an unprecedented possibility to test both the vortex and crystal dynamics during a glitch. Here, we explore the glitch dependence on the supersolid quality, finding strong suppression at the supersolid-to-solid transition. This provides a tool to study glitches originating from different radial depths of a neutron star. Benchmarking our theory against neutron star observations, our work will open a new avenue for the quantum simulation of stellar objects from Earth.
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M. Sohmen, M. J. Mark, M. Greiner, F. Ferlaino A ship-in-a-bottle quantum gas microscope for magnetic mixtures.,
SciPost Phys. 15 182 (2023-11-01),
http://dx.doi.org/10.21468/SciPostPhys.15.5.182 doi:10.21468/SciPostPhys.15.5.182 (ID: 721179)
Toggle Abstract
Quantum gas microscopes are versatile and powerful tools for fundamental science as well as promising candidates for enticing applications such as in quantum simulation or quantum computation. Here we present a quantum gas microscopy setup for experiments with highly magnetic atoms of the lanthanoid elements erbium and dysprosium. Our setup features a non-magnetic, non-conducting, large-working-distance, high-numerical-aperture, in-vacuum microscope objective, mounted inside a glue-free quartz glass cell. The quartz glass cell is enclosed by a compact multi-shell ferromagnetic shield that passively suppresses external magnetic field noise by a factor of more than a thousand. Our setup will enable direct manipulation and probing of the rich quantum many-body physics of dipolar atoms in optical lattices, and bears the potential to put exciting theory proposals - including exotic magnetic phases and quantum phase transitions - to an experimental test.
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L. Su, A. Douglas, M. Szurek, R. Groth, F. Ozturk, A. Krahn, A. Hébert, G. Phelps, S. Ebadi, S. Dickerson, F. Ferlaino, O. Markovic, M. Greiner Dipolar quantum solids emerging in a Hubbard quantum simulator,
Nature 622 729 (2023-10-25),
http://dx.doi.org/10.1038/s41586-023-06614-3 doi:10.1038/s41586-023-06614-3 (ID: 721126)
Toggle Abstract
In quantum mechanical many-body systems, long-range and anisotropic interactions promote rich spatial structure and can lead to quantum frustration, giving rise to a wealth of complex, strongly correlated quantum phases. Long-range interactions play an important role in nature; however, quantum simulations of lattice systems have largely not been able to realize such interactions. A wide range of efforts are underway to explore long-range interacting lattice systems using polar molecules, Rydberg atoms, optical cavities, and magnetic atoms. Here, we realize novel quantum phases in a strongly correlated lattice system with long-range dipolar interactions using ultracold magnetic erbium atoms. As we tune the dipolar interaction to be the dominant energy scale in our system, we observe quantum phase transitions from a superfluid into dipolar quantum solids, which we directly detect using quantum gas microscopy with accordion lattices. Controlling the interaction anisotropy by orienting the dipoles enables us to realize a variety of stripe ordered states. Furthermore, by transitioning non-adiabatically through the strongly correlated regime, we observe the emergence of a range of metastable stripe-ordered states. This work demonstrates that novel strongly correlated quantum phases can be realized using long-range dipolar interaction in optical lattices, opening the door to quantum simulations of a wide range of lattice models with long-range and anisotropic interactions.
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B. Blakie, L. Chomaz, D. Baillie, F. Ferlaino Compressibility and speeds of sound across the superfluid-to-supersolid phase transition of an elongated dipolar gas,
Phys. Rev. Research (2023-09-06),
http://dx.doi.org/10.1103/PhysRevResearch.5.033161 doi:10.1103/PhysRevResearch.5.033161 (ID: 721177)
Toggle Abstract
We investigate the excitation spectrum and compressibility of a dipolar Bose-Einstein condensate in an infinite tube potential in the parameter regime where the transition between superfluid and supersolid phases occurs. Our study focuses on the density range in which crystalline order develops continuously across the transition. Above the transition the superfluid shows a single gapless excitation band, phononic at small momenta and with a roton at a finite momentum. Below the transition, two gapless excitations branches (three at the transition point) emerge in the supersolid. We examine the two gapless excitation bands and their associated speeds of sound in the supersolid phase. Our results show that the speeds of sound and the compressibility are discontinuous at the transition, indicating a second-order phase transition. These results provide valuable insights into the identification of supersolid phenomena in dipolar quantum gases and the relationship to supersolidity in spin-orbit coupled gases.
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T. Bland, G. Lamporesi, M. J. Mark, F. Ferlaino Vortices in dipolar Bose–Einstein condensates,
Comptes Rendus Physique 24 20 (2023-09-05),
http://dx.doi.org/10.5802/crphys.160 doi:10.5802/crphys.160 (ID: 721125)
Toggle Abstract
Quantized vortices are the hallmark of superfluidity, and are often sought out as the first observable feature in new superfluid systems. Following the recent experimental observation of vortices in Bose–Einstein condensates comprised of atoms with inherent long-range dipole-dipole interactions [Nat. Phys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the three-dimensional dominantly dipolar regime, where beyond-mean-field effects are crucial for stability, and investigate the interplay between trap geometry and magnetic field tilt angle.
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J. Sánchez-Baena, C. Politi, F. Maucher, F. Ferlaino, T. Pohl Heating a quantum dipolar fluid into a solid,
Nat. Commun. 14 1868 (2023-04-04),
http://dx.doi.org/10.1038/s41467-023-37207-3 doi:10.1038/s41467-023-37207-3 (ID: 720879)
Toggle Abstract
Raising the temperature of a material enhances the thermal motion of particles. Such an increase in thermal energy commonly leads to the melting of a solid into a fluid and eventually vaporises the liquid into a gaseous phase of matter. Here, we study the finite-temperature physics of dipolar quantum fluids and find surprising deviations from this general phenomenology. In particular, we describe how heating a dipolar superfluid from near-zero temperatures can induce a phase transition to a supersolid state with a broken translational symmetry. The predicted effect agrees with experimental measurements on ultracold dysprosium atoms, which opens the door for exploring the unusual thermodynamics of dipolar quantum fluids.
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L. Chomaz, I. Ferrier-Barbut, F. Ferlaino, B. Laburthe-Tolra, B. L. Lev, T. Pfau Dipolar physics: A review of experiments with magnetic quantum gases.,
Rep. Prog. Phys. 86 (2022-12-30),
http://dx.doi.org/10.1088/1361-6633/aca814 doi:10.1088/1361-6633/aca814 (ID: 720740)
Toggle Abstract
Since the achievement of quantum degeneracy in gases of chromium atoms in 2004, the experimental investigation of ultracold gases made of highly magnetic atoms has blossomed. The field has yielded the observation of many unprecedented phenomena, in particular those in which long-range and anisotropic dipole-dipole interactions play a crucial role. In this review, we aim to present the aspects of the magnetic quantum-gas platform that make it unique for exploring ultracold and quantum physics as well as to give a thorough overview of experimental achievements.<br />
Highly magnetic atoms distinguish themselves by the fact that their electronic ground-state configuration possesses a large spin (as well as a large g factor). This results in a large magnetic moment and a rich electronic transition spectrum. Such transitions are useful for cooling, trapping, and manipulating these atoms. The complex atomic structure and large dipolar moments of these atoms also lead to a dense spectrum of resonances in their two-body scattering behaviour. These resonances can be used to control the interatomic interactions and, in particular, the relative importance of contact over dipolar interactions. These features provide exquisite control knobs for exploring the few- and many-body physics of dipolar quantum gases.<br />
The study of dipolar effects in magnetic quantum gases has covered various few-body phenomena that are based on elastic and inelastic anisotropic scattering. Various many-body effects have also been demonstrated. These affect both the shape, stability, dynamics, and excitations of fully polarised repulsive Bose or Fermi gases. Beyond the mean-field instability, strong dipolar interactions competing with slightly weaker contact interactions between magnetic bosons yield new quantum stabilised states, among which self-bound droplets, droplet assemblies, and supersolids. Dipolar interactions also deeply affect the physics of atomic gases with an internal degree of freedom as these interactions intrinsically couple spin and atomic motion. Finally, long-range dipolar interactions can stabilise strongly correlated excited states of 1D gases and also impact the physics of lattice-confined systems, both at the spin-polarised level (Hubbard models with off-site interactions) and at the spinful level (XYZ models). In the present manuscript, we aim to provide an extensive overview of the various related experimental achievements up to the present.
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T. Bland, E. Poli, L. Peña Ardila, L. Santos, F. Ferlaino, R. N. Bisset Alternating-domain supersolids in binary dipolar condensates,
Phys. Rev. A 106 53322 (2022-11-30),
http://dx.doi.org/10.1103/PhysRevA.106.053322 doi:10.1103/PhysRevA.106.053322 (ID: 720839)
Toggle Abstract
Two-component dipolar condensates are now experimentally producible, and we theoretically investigate the nature of supersolidity in this system. We predict the existence of a binary supersolid state in which the two components form a series of alternating domains, producing an immiscible double supersolid. Remarkably, we find that a dipolar component can even induce supersolidity in a nondipolar component. In stark contrast to single-component supersolids, the number of crystal sites is not strictly limited by the condensate populations, and the density is hence substantially lower. Our results are applicable to a wide range of dipole moment combinations, marking an important step towards long-lived bulk-supersolidity.
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L. Klaus, T. Bland, E. Poli, C. Politi, G. Lamporesi, E. Casotti, R. N. Bisset, M. J. Mark, F. Ferlaino Observation of vortices and vortex stripes in a dipolar condensate,
Nature Phys. 18 1458 (2022-10-31),
http://dx.doi.org/10.1038/s41567-022-01793-8 doi:10.1038/s41567-022-01793-8 (ID: 720846)
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G. Natale, T. Bland, Simon Gschwendtner, Louis Lafforgue, Daniel S. Grün, A. Patscheider, Manfred J. Mark, F. Ferlaino Bloch oscillations and matter-wave localization of a dipolar quantum gas in a one-dimensional lattice,
Communications Physics 5 227 (2022-09-15),
http://dx.doi.org/10.1038/s42005-022-01009-8 doi:10.1038/s42005-022-01009-8 (ID: 720840)
Toggle Abstract
Three-dimensional quantum gases of strongly dipolar atoms can undergo a crossover from a dilute gas to a dense macrodroplet, stabilized by quantum fluctuations. Adding a one-dimensional optical lattice creates a platform where quantum fluctuations are still unexplored, and a rich variety of new phases may be observable. We employ Bloch oscillations as an interferometric tool to assess the role quantum fluctuations play in an array of quasi-two-dimensional Bose-Einstein condensates. Long-lived oscillations are observed when the chemical potential is balanced between sites, in a region where a macrodroplet is extended over several lattice sites. Further, we observe a transition to a state that is localized to a single lattice plane−driven purely by interactions−marked by the disappearance of the interference pattern in the momentum distribution. To describe our observations, we develop a discrete one-dimensional extended Gross-Pitaevskii theory, including quantum fluctuations and a variational approach for the on-site wavefunction. This model is in quantitative agreement with the experiment, revealing the existence of single and multisite macrodroplets, and signatures of a two-dimensional bright soliton.
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M. Norcia, E. Poli, C. Politi, L. Klaus, T. Bland, M. J. Mark, L. Santos, R. N. Bisset, F. Ferlaino Can angular oscillations probe superfluidity in dipolar supersolids?,
Phys. Rev. Lett. 129 40403 (2022-07-22),
http://dx.doi.org/10.1103/PhysRevLett.129.040403 doi:10.1103/PhysRevLett.129.040403 (ID: 720697)
Toggle Abstract
Angular oscillations can provide a useful probe of the superfluid properties of a system. Such<br />
measurements have recently been applied to dipolar supersolids, which exhibit both density modulation and phase coherence, and for which robust probes of superfluidity are particularly interesting.<br />
So far, these investigations have been confined to linear droplet arrays. Here, we explore angular<br />
oscillations in systems with 2D structure, which in principle have greater sensitivity to superfluidity.<br />
Surprisingly, in both experiment and simulation, we find that the frequency of angular oscillations<br />
remains nearly unchanged even when the superfluidity of the system is altered dramatically. This<br />
indicates that angular oscillation measurements do not always provide a robust experimental probe<br />
of superfluidity with typical experimental protocols.
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S. Julia-Farre, D. Gonzalez-Cuadra, A. Patscheider, M. J. Mark, F. Ferlaino, M. Lewenstein, L. Barbiero, A. Dauphin Revealing the topological nature of the bond order wave in a strongly correlated quantum system,
Phys. Rev. Research 4 L032005 (2022-07-08),
http://dx.doi.org/10.1103/PhysRevResearch.4.L032005 doi:10.1103/PhysRevResearch.4.L032005 (ID: 720727)
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A. Patscheider, L. Chomaz, G. Natale, D. Petter, M. J. Mark, S. Baier, B. Yang, R. R. Wang, J. L. Bohn, F. Ferlaino Determination of the scattering length of erbium atoms,
Phys. Rev. A 105 63307 (2022-06-08),
http://dx.doi.org/10.1103/PhysRevA.105.063307 doi:10.1103/PhysRevA.105.063307 (ID: 720739)
Toggle Abstract
An accurate knowledge of the scattering length is fundamental in ultracold quantum gas experiments and essential for the characterisation of the system as well as for a meaningful comparison to theoretical models. Here, we perform a careful characterisation of the s-wave scattering length as for the four highest-abundance isotopes of erbium, in the magnetic field range from 0 G to 5 G. We report on cross-dimensional thermalization measurements and apply the Enskog equations of change to numerically simulate the thermalization process and to analytically extract an expression for the so-called number of collisions per re-thermalization (NCPR) to obtain as from our experimental data. We benchmark the applied cross-dimensional thermalization technique with the experimentally more demanding lattice modulation spectroscopy and find good agreement for our parameter regime. Our experiments are compatible with a dependence of the NCPR with as, as theoretically expected in the case of strongly dipolar gases. Surprisingly, we experimentally observe a dependency of the NCPR on the density, which might arise due to deviations from an ideal harmonic trapping configuration. Finally, we apply a model for the dependency of the background scattering length with the isotope mass, allowing to estimate the number of bound states of erbium.
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T. Bland, E. Poli, C. Politi, L. Klaus, M. Norcia, F. Ferlaino, L. Santos, R. N. Bisset Two-Dimensional Supersolid Formation in Dipolar Condensates,
Phys. Rev. Lett. 128 195302 (2022-05-13),
http://dx.doi.org/10.1103/PhysRevLett.128.195302 doi:10.1103/PhysRevLett.128.195302 (ID: 720678)
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C. Politi, A. Trautmann, P. Ilzhöfer, G. Durastante, M. J. Mark, M. Mondugno, F. Ferlaino Interspecies interactions in an ultracold dipolar mixture,
Phys. Rev. A (2022-02-03),
http://dx.doi.org/10.1103/PhysRevA.105.023304 doi:10.1103/PhysRevA.105.023304 (ID: 720698)
Toggle Abstract
We experimentally and theoretically investigate the influence of the dipole-dipole interactions (DDIs) on the total interspecies interaction in an erbium-dysprosium mixture. By rotating the dipole orientation we are able to tune the effect of the long-range and anisotropic DDI, and therefore the in-trap displacements of the erbium and dysprosium clouds. We present a theoretical description for our binary system based on an extended Gross-Pitaevskii theory, including the single-species beyond mean-field terms, and we predict a lower and an upper bound for the interspecies scattering length
a
12
=
105
[
−
65
,
+
162
]
a
0
. Our work is a step towards the investigation of the experimentally unexplored dipolar miscibility-immiscibility phase diagram and the realization of quantum droplets and supersolid states with heteronuclear dipolar mixtures.
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E. Poli, T. Bland, C. Politi, L. Klaus, M. Norcia, F. Ferlaino, R. N. Bisset, L. Santos Maintaining supersolidity in one and two dimensions,
Phys. Rev. A 104 63307 (2021-12-09),
http://dx.doi.org/10.1103/PhysRevA.104.063307 doi:10.1103/PhysRevA.104.063307 (ID: 720729)
Toggle Abstract
We theoretically investigate supersolidity in three-dimensional dipolar Bose-Einstein condensates. We focus on the role of trap geometry in determining the dimensionality of the resulting droplet arrays, which range from one-dimensional to zigzag, through to two-dimensional supersolids in circular traps. Supersolidity is well established in one-dimensional arrays, and may be just as favorable in two-dimensional arrays provided that one appropriately scales the atom number to the trap volume. We develop a tractable variational model—which we benchmark against full numerical simulations—and use it to study droplet crystals and their excitations. We also outline how exotic ring and stripe states may be created with experimentally feasible parameters. Our work paves the way for future studies of two-dimensional dipolar supersolids in realistic settings.
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M. Norcia, F. Ferlaino Developments in atomic control using ultracold magnetic lanthanides,
Nature Phys. 17 1357 (2021-11-25),
http://dx.doi.org/10.1038/s41567-021-01398-7 doi:10.1038/s41567-021-01398-7 (ID: 720728)
Toggle Abstract
Lanthanide atoms have an unusual electron configuration, with a partially filled shell of f orbitals. This leads to a set of characteristic properties, including large numbers of optical transitions with widely varying wavelengths and transition strengths, anisotropic interaction properties between atoms and with light, and a large magnetic moment and spin space present in the ground state, that enable enhanced control over ultracold atoms and their interactions. These features, in turn, enable new forms of control as well as novel many-body phenomena. Microkelvin temperatures can be reached by narrow-line laser cooling and evaporative cooling through universal dipolar scattering. The properties and tunability of the interatomic interactions have enabled observations of a rotonic dispersion relation, self-bound liquid-like droplets stabilized by quantum fluctuations and supersolid states. Here we describe how the unusual level structure of lanthanide atoms leads to these key features and provide a brief and necessarily partial overview of experimental progress in this rapidly developing field.
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A. Patscheider, B. Yang, G. Natale, D. Petter, L. Chomaz, M. J. Mark, G. Hovhannesyan, M. Lepers, F. Ferlaino Observation of a narrow inner-shell orbital transition in atomic erbium at 1299 nm,
Phys. Rev. Research 3 33256 (2021-09-17),
http://dx.doi.org/10.1103/PhysRevResearch.3.033256 doi:10.1103/PhysRevResearch.3.033256 (ID: 720648)
Toggle Abstract
We report on the observation and coherent excitation of atoms on the narrow inner-shell orbital transition, connecting the erbium ground state [Xe]4f12(3H6)6s2 to the excited state [Xe]4f11(4I15/2)05d(5D3/2)6s2(15/2,3/2)07. This transition corresponds to a wavelength of 1299 nm and is optically closed. We perform high-resolution spectroscopy to extract the gJ-factor of the 1299-nm state and to determine the frequency shift for four bosonic isotopes. We further demonstrate coherent control of the atomic state and extract a lifetime of 178(19) ms which corresponds to a linewidth of 0.9(1) Hz. The experimental findings are in good agreement with our semi-empirical model. In addition, we present theoretical calculations of the atomic polarizability, revealing several different magic-wavelength conditions. Finally, we make use of the vectorial polarizability and confirm a possible magic wavelength at 532 nm.
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A. Trautmann, M. J. Mark, P. Ilzhöfer, H. Edri, A. El Arrach, J. G. Maloberti, C. Greene, F. Robicheaux, F. Ferlaino Spectroscopy of Rydberg States in Erbium using Electromagnetically Induced Transparency,
Phys. Rev. Research 3 33165 (2021-08-19),
http://dx.doi.org/10.1103/PhysRevResearch.3.033165 doi:10.1103/PhysRevResearch.3.033165 (ID: 720647)
Toggle Abstract
We present a study of the Rydberg spectrum in 166Er for series connected to the 4f12(3H6)6s, Jc=13/2 and Jc=11/2 ionic core states using an all-optical detection based on electromagnetically induced transparency in an effusive atomic beam. Identifying approximately 550 individual states, we find good agreement with a multi-channel quantum defect theory (MQDT) which allows assignment of most states to ns or nd Rydberg series. We provide an improved accuracy for the lowest two ionization thresholds to EIP,Jc=13/2=49260.750(1)cm-1 and EIP,Jc=11/2=49701.184(1)cm-1 as well as the corresponding quantum defects for all observed series. We identify Rydberg states in five different isotopes, and states between the two lowest ionization thresholds. Our results open the way for future applications of Rydberg states for quantum simulation using erbium and exploiting its special open-shell structure.
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M. Norcia, C. Politi, L. Klaus, E. Poli, M. Sohmen, M. J. Mark, R. N. Bisset, L. Santos, F. Ferlaino Two-dimensional supersolidity in a dipolar quantum gas,
Nature 596 361 (2021-08-18),
http://dx.doi.org/10.1038/s41586-021-03725-7 doi:10.1038/s41586-021-03725-7 (ID: 720624)
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D. Petter, A. Patscheider, G. Natale, M. J. Mark, M. Baranov, R. van Bijnen, S. M. Roccuzzo, A. Recati, B. Blakie, D. Baillie, L. Chomaz, F. Ferlaino Bragg scattering of an ultracold dipolar gas across the phase transition from Bose-Einstein condensate to supersolid in the free-particle regime,
Phys. Rev. A 104 L011302 (2021-07-22),
http://dx.doi.org/10.1103/PhysRevA.104.L011302 doi:10.1103/PhysRevA.104.L011302 (ID: 720484)
Toggle Abstract
We present an experimental and theoretical study of the high-energy excitation spectra of a dipolar supersolid. Using Bragg spectroscopy, we study the scattering response of the system to a high-energy probe, enabling measurements of the dynamic structure factor. We experimentally observe a continuous reduction of the response when tuning the contact interaction from an ordinary Bose-Einstein condensate to a supersolid state. Yet the observed reduction is faster than the one theoretically predicted by the Bogoliubov-de-Gennes theory. Based on an intuitive semi-analytic model and real-time simulations, we primarily attribute such a discrepancy to the out-of-equilibrium phase dynamics, which although not affecting the system global coherence, reduces its response.
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M. Sohmen, C. Politi, L. Klaus, L. Chomaz, M. J. Mark, M. Norcia, F. Ferlaino Birth, life, and death of a dipolar supersolid,
Phys. Rev. Lett. 126 233401 (2021-06-07),
http://dx.doi.org/10.1103/PhysRevLett.126.233401 doi:10.1103/PhysRevLett.126.233401 (ID: 720625)
Toggle Abstract
In the short time since the first observation of supersolid states of ultracold dipolar atoms, substantial progress has been made in understanding the zero-temperature phase diagram and low-energy excitations of these systems. Less is known, however, about their finite-temperature properties, particularly relevant for supersolids formed by cooling through direct evaporation. Here, we explore this realm by characterizing the evaporative formation and subsequent decay of a dipolar supersolid by combining high-resolution in-trap imaging with time-of-flight observables. As our atomic system cools toward quantum degeneracy, it first undergoes a transition from thermal gas to a crystalline state with the appearance of periodic density modulation. This is followed by a transition to a supersolid state with the emergence of long-range phase coherence. Further, we explore the role of temperature in the development of the modulated state.
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P. Ilzhöfer, M. Sohmen, G. Durastante, C. Politi, A. Trautmann, G. Morpurgo, T. Giamarchi, L. Chomaz, M. J. Mark, F. Ferlaino Phase coherence in out-of-equilibrium supersolid states of ultracold dipolar atoms,
Nature Phys. 17 361 (2021-01-04),
http://dx.doi.org/10.1038/s41567-020-01100-3 doi:10.1038/s41567-020-01100-3 (ID: 720437)
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L. R. Picard, M. J. Mark, F. Ferlaino, R. van Bijnen Deep Learning-Assisted Classification of Site-Resolved Quantum Gas Microscope Images,
Measurement Science and Technology 31 25201 (2019-11-05),
http://dx.doi.org/10.1088/1361-6501/ab44d8 doi:10.1088/1361-6501/ab44d8 (ID: 720262)
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G. Natale, R. van Bijnen, A. Patscheider, D. Petter, M. J. Mark, L. Chomaz, F. Ferlaino Excitation spectrum of a trapped dipolar supersolid and its experimental evidence,
Phys. Rev. Lett. 123 50402 (2019-08-01),
http://dx.doi.org/10.1103/PhysRevLett.123.050402 doi:10.1103/PhysRevLett.123.050402 (ID: 720313)
Toggle Abstract
We study the spectrum of elementary excitations of a trapped dipolar Bose gas across the superfluid-supersolid phase transition. Our calculations, accounting for the experimentally relevant case of confined systems, show that, when entering the supersolid phase, two distinct excitation branches appear, respectively connected to crystal or superfluid orders. These results confirm infinite-system predictions, showing that finite-size effects play only a small qualitative role. Experimentally, we probe compressional excitations in an Er quantum gas across the phase diagram. While in the BEC regime the system exhibits an ordinary quadrupole oscillation, in the supersolid regime, we observe a striking two-frequency response of the system, related to the two spontaneously broken symmetries.
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D. Petter, G. Natale, R. van Bijnen, A. Patscheider, M. J. Mark, L. Chomaz, F. Ferlaino Probing the roton excitation spectrum of a stable dipolar Bose gas,
Phys. Rev. Lett. 122 183401 (2019-05-08),
http://dx.doi.org/10.1103/PhysRevLett.122.183401 doi:10.1103/PhysRevLett.122.183401 (ID: 720098)
Toggle Abstract
We measure the excitation spectrum of a stable dipolar Bose--Einstein condensate over a wide momentum-range via Bragg spectroscopy. We precisely control the relative strength, εdd, of the dipolar to the contact interactions and observe that the spectrum increasingly deviates from the linear phononic behavior for increasing εdd. Reaching the dipolar dominated regime εdd>1, we observe the emergence of a roton minimum in the spectrum and its softening towards instability. We characterize how the excitation energy and the strength of the density-density correlations at the roton momentum vary with εdd. Our findings are in excellent agreement with numerical calculations based on mean-field Bogoliubov theory. When including beyond-mean-field corrections, in the form of a Lee-Huang-Yang potential, we observe a quantitative deviation from the experiment, questioning the validity of such a description in the roton regime.
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L. Chomaz, D. Petter, P. Ilzhöfer, G. Natale, A. Trautmann, C. Politi, G. Durastante, R. van Bijnen, A. Patscheider, M. Sohmen, M. J. Mark, F. Ferlaino Long-Lived and Transient Supersolid Behaviors in Dipolar Quantum Gases,
Phys. Rev. X 9 21012 (2019-04-19),
http://dx.doi.org/10.1103/PhysRevX.9.021012 doi:10.1103/PhysRevX.9.021012 (ID: 720203)
Toggle Abstract
By combining theory and experiments, we demonstrate that dipolar quantum gases of both 166Er and 164Dy support a state with supersolid properties, where a spontaneous density modulation and a global phase coherence coexist. This paradoxical state occurs in a well defined parameter range, separating the phases of a regular Bose-Einstein condensate and of an insulating droplet array, and is rooted in the roton mode softening, on the one side, and in the stabilization driven by quantum fluctuations, on the other side. Here, we identify the parameter regime for each of the three phases. In the experiment, we rely on a detailed analysis of the interference patterns resulting from the free expansion of the gas, quantifying both its density modulation and its global phase coherence. Reaching the phases via a slow interaction tuning, starting from a stable condensate, we observe that 166Er and 164Dy exhibit a striking difference in the lifetime of the supersolid properties, due to the different atom loss rates in the two systems. Indeed, while in 166Er the supersolid behavior only survives a few tens of milliseconds, we observe coherent density modulations for more than 150ms in 164Dy. Building on this long lifetime, we demonstrate an alternative path to reach the supersolid regime, relying solely on evaporative cooling starting from a thermal gas.
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A. Trautmann, P. Ilzhöfer, G. Durastante, C. Politi, M. Sohmen, M. J. Mark, F. Ferlaino Dipolar Quantum Mixtures of Erbium and Dysprosium Atoms,
Phys. Rev. Lett. 121 213601 (2018-11-21),
http://dx.doi.org/10.1103/PhysRevLett.121.213601 doi:10.1103/PhysRevLett.121.213601 (ID: 720050)
Toggle Abstract
We report on the first realization of heteronuclear dipolar quantum mixtures of highly magnetic erbium and dysprosium atoms. With a versatile experimental setup, we demonstrate binary Bose-Einstein condensation in five different Er-Dy isotope combinations, as well as one Er-Dy Bose-Fermi mixture. Finally, we present first studies of the interspecies interaction between the two species for one mixture.
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S. Baier, D. Petter, J. H. Becher, A. Patscheider, G. Natale, L. Chomaz, M. J. Mark, F. Ferlaino Realization of a Strongly Interacting Fermi Gas of Dipolar Atoms,
Phys. Rev. Lett. 121 93602 (2018-08-29),
http://dx.doi.org/10.1103/PhysRevLett.121.093602 doi:10.1103/PhysRevLett.121.093602 (ID: 720004)
Toggle Abstract
We realize a two-component dipolar Fermi gas with tunable interactions, using erbium atoms. Employing a lattice-protection technique, we selectively prepare deeply degenerate mixtures of the two lowest spin states and perform high-resolution Feshbach spectroscopy in an optical dipole trap. We identify a comparatively broad Feshbach resonance and map the interspin scattering length in its vicinity. The Fermi mixture shows a remarkable collisional stability in the strongly interacting regime, providing a first step towards studies of superfluid pairing, crossing from Cooper pairs to bound molecules, in presence of dipole-dipole interactions.
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V. Veljic, A. R. Lima, L. Chomaz, S. Baier, M. J. Mark, F. Ferlaino, A. Pelster, A. Balaz Ground state of an ultracold Fermi gas of tilted dipoles,
New J. Phys. 20 93016 (2018-06-14),
http://dx.doi.org/10.1088/1367-2630/aade24 doi:10.1088/1367-2630/aade24 (ID: 720051)
Toggle Abstract
Many-body dipolar effects in Fermi gases are quite subtle as they energetically compete with the large kinetic energy at and below the Fermi surface (FS). Recently it was experimentally observed that its FS is deformed from a sphere to an ellipsoid due to the presence of the anisotropic and long-range dipole-dipole interaction. Moreover, it was suggested that, when the dipoles are rotated by means of an external field, the Fermi surface follows their rotation, thereby keeping the major axis of the momentum-space ellipsoid parallel to the dipoles. Here we generalise a previous Hartree-Fock mean-field theory to systems confined in an elongated triaxial trap with an arbitrary orientation of the dipoles relative to the trap. With this we study for the first time the effects of the dipoles' arbitrary orientation on the ground-state properties of the system. Furthermore, taking into account the geometry of the system, we show how the ellipsoidal FS deformation can be reconstructed, assuming ballistic expansion, from the experimentally measurable real-space aspect ratio after a free expansion. We compare our theoretical results with new experimental data measured with erbium Fermi gas for various trap parameters and dipole orientations. The observed remarkable agreement demonstrates the ability of our model to capture the full angular dependence of the FS deformation. Moreover, for systems with even higher dipole moment, our theory predicts an additional unexpected effect: the FS does not simply follow rigidly the orientation of the dipoles but softens showing a change in the aspect ratio depending on the dipoles' orientation relative to the trap geometry, as well as on the trap anisotropy itself. Our theory provides the basis for understanding and interpreting phenomena in which the investigated physics depends on the underlying structure of the FS, such as fermionic pairing and superfluidity.
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L. Chomaz, R. van Bijnen, D. Petter, G. Faraoni, S. Baier, M. J. Mark, F. Wächtler, L. Santos, F. Ferlaino Observation of roton mode population in a dipolar quantum gas,
Nature Phys. 14 446 (2018-03-05),
http://dx.doi.org/10.1038/s41567-018-0054-7 doi:10.1038/s41567-018-0054-7 (ID: 719813)
Toggle Abstract
The concept of a roton, a special kind of elementary excitation, forming a minimum of energy at finite momentum, has been essential to understand the properties of superfluid 4He. In quantum liquids, rotons arise from strong interparticle interactions, whose microscopic description remains debated. In the realm of highly-controllable quantum gases, a roton mode has been predicted to emerge due to dipolar interparticle interactions despite of their weakly-interacting character. Yet it has remained elusive to observations. Here we report momentum-distribution measurements in dipolar quantum gases of highly-magnetic erbium atoms, revealing the existence of the long-sought roton. We observe the appearance of peculiar peaks at well-defined momentum matching the inverse of the tight confinement length as expected for dipolar rotons. Our combined theoretical and experimental work demonstrates unambiguously the roton softening of the excitation spectrum and provides a further step in the quest towards supersolidity.
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P. Ilzhöfer, G. Durastante, A. Patscheider, A. Trautmann, M. J. Mark, F. Ferlaino Two-species five-beam magneto-optical trap for erbium and dysprosium,
Phys. Rev. A 97 23633 (2018-02-26),
http://dx.doi.org/10.1103/PhysRevA.97.023633 doi:10.1103/PhysRevA.97.023633 (ID: 719919)
Toggle Abstract
We report on the first realization of a two-species magneto-optical trap (MOT) for erbium and dysprosium. The MOT operates on an intercombination line for the respective species. Owing to the narrow-line character of such a cooling transition and the action of gravity, we demonstrate a novel trap geometry employing only five beams in orthogonal configuration. We observe that the mixture is cooled and trapped very efficiently, with up to \num{5e8} Er atoms and \num{e9} Dy atoms at temperatures of about 10μK. Our results offer an ideal starting condition for the creation of a dipolar quantum mixture of highly magnetic atoms.
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J. H. Becher, S. Baier, K. Aikawa, M. Lepers, J. Wyart, O. Dulieu, F. Ferlaino Anisotropic polarizability of erbium atoms,
Phys. Rev. A 97 12509 (2018-01-19),
http://dx.doi.org/10.1103/PhysRevA.97.012509 doi:10.1103/PhysRevA.97.012509 (ID: 719925)
Toggle Abstract
We report on the determination of the dynamical polarizability of ultracold erbium atoms in the ground and in one excited state at three different wavelengths, which are particularly relevant for optical trapping. Our study combines experimental measurements of the light shift and theoretical calculations. In particular, our experimental approach allows us to isolate the different contributions to the polarizability, namely the isotropic scalar and anisotropic tensor part. For the latter contribution, we observe a clear dependence of the atomic polarizability on the angle between the laser-field-polarization axis and the quantization axis, set by the external magnetic field. Such an angle-dependence is particularly pronounced in the excited-state polarizability. We compare our experimental findings with the theoretical values, based on semi-empirical electronic-structure calculations and we observe a very good overall agreement. Our results pave the way to exploit the anisotropy of the tensor polarizability for spin-selective preparation and manipulation.
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F. Ferlaino The Discreet Charm of Dipolar Quantum Matter near Absolute Zero Temperature,
Colloquium Università Trento (Trento, 2016-09-28) URL (2016-09-28),
(ID: 719665)
Toggle Abstract
Approaching temperatures near the absolute zero, i.e. the lowest temperature in the whole universe, the atoms develop extreme behaviors, which challenge our understanding. In this extreme regime, the atoms assume exceptional behaviors and form a new
type of matter, which is now governed by the laws of quantum mechanics. In this regime, the interactions between many particles dictate the quantum behavior. Highly magnetic atoms, such as Erbium, endow a novel type of interaction to the quantum behavior, namely the dipole-dipole interaction (DDI). Because of its long-range nature and an isotropic character, the DDI imprints genuinely novel properties at the many- and few-body level. The behavior of these systems is fundamental to understand nature and quantum physics, and reserves us every day fascinating and counterintuitive surprises. This talk will provide an overview of the fascinating dipolar phenomena from the Innsbruck prospective, ranging from the first-produced quantum gas of Er, to the observation of chaotic scattering and the formation of a quasi self-bound droplet state in analogy with the He case.
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F. Ferlaino The Discreet Charm of Dipolar Quantum Matter near Absolute Zero Temperature,
Physikkolloquium Universität Heidelberg (Heidelberg) (2016-07-01),
(ID: 719623)
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F. Ferlaino The Fascination of Lanthanides for Ultracold Quantum Physics,
Kolloquium Humboldt-Universitaet zu Berlin (Berlin) (2016-01-12),
(ID: 719447)
Toggle Abstract
Given their strong magnetic moment and exotic electronic configuration, lanthanide atomic species disclose a plethora of intriguing phenomena in ultracold quantum physics. The large magnetic moment of these atoms reflects on a strong interparticle dipole-dipole interaction, which has both a long-range nature and an isotropic character. Here, we report on our latest results on quantum many-body and few-body physics based on a strongly-magnetic lanthanide, erbium (Er). Particular emphasis will be given to the scattering properties of bosonic and fermionic Er, in which unconventional and fascinating phenomena appear as a result of both the magnetic and the orbital anisotropy of the underlying the native interactions between atoms.
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K. Aikawa, A. Frisch, M. Mark, S. Baier, R. Grimm, J. L. Bohn, D. S. Jin, G. Bruun, F. Ferlaino Anisotropic Relaxation Dynamics in a Dipolar Fermi Gas Driven Out of Equilibrium,
Phys. Rev. Lett. 113 263201 (2014-12-23),
http://dx.doi.org/10.1103/PhysRevLett.113.263201 doi:10.1103/PhysRevLett.113.263201 (ID: 718908)
Toggle Abstract
We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic Er167 fermions, spin polarized in the lowest Zeeman sublevel. In this system, elastic collisions arise purely from universal dipolar scattering. Based on cross-dimensional rethermalization experiments, we observe a strong anisotropy of the scattering, which manifests itself in a large angular dependence of the thermal relaxation dynamics. Our result is in good agreement with recent theoretical predictions. Furthermore, we measure the rethermalization rate as a function of temperature for different angles and find that the suppression of collisions by Pauli blocking is not influenced by the dipole orientation.
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T. Takekoshi, L. Reichsöllner, A. Schindewolf, J. M. Hutson, C. Le Sueur, O. Dulieu, F. Ferlaino, R. Grimm, H. Nägerl Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state,
Phys. Rev. Lett. 113 205301 (2014-11-12),
http://dx.doi.org/10.1103/PhysRevLett.113.205301 doi:10.1103/PhysRevLett.113.205301 (ID: 718921)
Toggle Abstract
We produce ultracold dense trapped samples of Rb87Cs133 molecules in their rovibrational ground state, with full nuclear hyperfine state control, by stimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We observe the onset of hyperfine-changing collisions when the magnetic field is ramped so that the molecules are no longer in the hyperfine ground state. A strong quadratic shift of the transition frequencies as a function of applied electric field shows the strongly dipolar character of the RbCs ground-state molecule. Our results open up the prospect of realizing stable bosonic dipolar quantum gases with ultracold molecules.
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K. Aikawa, S. Baier, A. Frisch, M. Mark, C. Ravensbergen, F. Ferlaino Observation of Fermi surface deformation in a dipolar quantum gas,
Science 345 6203 (2014-09-19),
http://dx.doi.org/10.1126/science.1255259 doi:10.1126/science.1255259 (ID: 718909)
Toggle Abstract
In the presence of isotropic interactions, the Fermi surface of an ultracold Fermi gas is spherical. Introducing anisotropic interactions can deform the Fermi surface, but the effect is subtle and challenging to observe experimentally. Here, we report on the observation of a Fermi surface deformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation is caused by the interplay between strong magnetic dipole-dipole interaction and the Pauli exclusion principle. We demonstrate the many-body nature of the effect and its tunability with the Fermi energy. Our observation provides a basis for future studies on anisotropic many-body phenomena in normal and superfluid phases.
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F. Ferlaino Molecular physics: Complexity trapped by simplicity,
Nature 512 262 (2014-08-20),
http://dx.doi.org/10.1038/512261a doi:10.1038/512261a (ID: 718990)
Toggle Abstract
Devices known as magneto-optical traps have long been used to cool and confine atoms, but not molecules — until now. This new ability should enable many studies and applications of the physics of ultracold molecules.
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A. Zenesini, B. Huang, M. Berninger, H. Nägerl, F. Ferlaino, R. Grimm Resonant atom-dimer collisions in cesium: Testing universality at positive scattering lengths,
Phys. Rev. A 90 022704 (2014-08-11),
http://dx.doi.org/10.1103/PhysRevA.90.022704 doi:10.1103/PhysRevA.90.022704 (ID: 718945)
Toggle Abstract
We study the collisional properties of an ultracold mixture of cesium atoms and dimers close to a Feshbach resonance near 550 G in the regime of positive s-wave scattering lengths. We observe an atom-dimer loss resonance that is related to Efimov's scenario of trimer states. The resonance is found at a value of the scattering length that is different from a previous observation at low magnetic fields. This indicates nonuniversal behavior of the Efimov spectrum for positive scattering lengths. We compare our observations with predictions from effective field theory and with a recent model based on the van der Waals interaction. We present additional measurements on pure atomic samples in order to check for the presence of a resonant loss feature related to an avalanche effect, as suggested by observations in other atomic species. We could not confirm the presence of such a feature.
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A. Frisch, M. Mark, K. Aikawa, F. Ferlaino, J. L. Bohn, C. Makrides, A. Petrov, S. Kotochigova Quantum Chaos in Ultracold Collisions of Erbium,
Nature 507 479 (2014-03-27),
http://dx.doi.org/10.1038/nature13137 doi:10.1038/nature13137 (ID: 718682)
Toggle Abstract
Atomic and molecular samples reduced to temperatures below 1 microkelvin, yet still in the gas phase, afford unprecedented energy resolution in probing and manipulating how their constituent particles interact with one another. For simple atoms, such as alkalis, scattering resonances are extremely well-characterized. However, ultracold physics is now poised to enter a new regime, where far more complex species can be cooled and studied, including magnetic lanthanide atoms and even molecules. For molecules, it has been speculated that a dense forest of resonances in ultracold collision cross sections will likely express essentially random fluctuations, much as the observed energy spectra of nuclear scattering do. According to the Bohigas-Giannoni-Schmit conjecture, these fluctuations would imply chaotic dynamics of the underlying classical motion driving the collision. This would provide a paradigm shift in ultracold atomic and molecular physics, necessitating new ways of looking at the fundamental interactions of atoms in this regime, as well as perhaps new chaos-driven states of ultracold matter. In this report we provide the first experimental demonstration that random spectra are indeed found at ultralow temperatures. In the experiment, an ultracold gas of erbium atoms is shown to exhibit many Fano-Feshbach resonances, for bosons on the order of 3 per gauss. Analysis of their statistics verifies that their distribution of nearest-neighbor spacings is what one would expect from random matrix theory. The density and statistics of these resonances are explained by fully-quantum mechanical scattering calculations that locate their origin in the anisotropy of the atoms' potential energy surface. Our results therefore reveal for the first time chaotic behavior in the native interaction between ultracold atoms.
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K. Aikawa, A. Frisch, M. Mark, S. Baier, R. Grimm, F. Ferlaino Reaching Fermi Degeneracy via Universal Dipolar Scattering,
Phys. Rev. Lett. 112 010404 (2014-01-06),
http://dx.doi.org/10.1103/PhysRevLett.112.010404 doi:10.1103/PhysRevLett.112.010404 (ID: 718621)
Toggle Abstract
We report on the creation of a degenerate dipolar Fermi gas of erbium atoms. We force evaporative cooling in a fully spin-polarized sample down to temperatures as low as 0.2 times the Fermi temperature. The strong magnetic dipole-dipole interaction enables elastic collisions between identical fermions even in the zero-energy limit. The measured elastic scattering cross section agrees well with the predictions from the dipolar scattering theory, which follow a universal scaling law depending only on the dipole moment and on the atomic mass. Our approach to quantum degeneracy proceeds with very high cooling efficiency and provides large atomic densities, and it may be extended to various dipolar systems.
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A. Frisch, K. Aikawa, F. Ferlaino, E. Berseneva, S. Kotochigova Hyperfine structure of laser-cooling transitions in fermionic erbium-167,
Phys. Rev. A 88 032508 (2013-09-13),
http://dx.doi.org/10.1103/PhysRevA.88.032508 doi:10.1103/PhysRevA.88.032508 (ID: 718495)
Toggle Abstract
We have measured and analyzed the hyperfine structure of two lines, one at 583 nm and one at 401 nm, of the only stable fermionic isotope of atomic erbium as well as determined its isotope shift relative to the four most-abundant bosonic isotopes. Our work focuses on the J→J+1 laser cooling transitions from the [Xe]4f126s2(3H6) ground state to two levels of the excited [Xe]4f126s6p configuration, which are of major interest for experiments on quantum degenerate dipolar Fermi gases. From a fit to the observed spectra of the strong optical transition at 401 nm we find that the magnetic dipole and electric quadrupole hyperfine constants for the excited state are Ae/h=−100.1(3) MHz and Be/h=−3079(30) MHz, respectively. The hyperfine spectrum of the narrow transition at 583 nm, was previously observed and accurate Ae and Be coefficients are available. A simulated spectrum based on these coefficients agrees well with our measurements. We have also determined the hyperfine constants using relativistic configuration-interaction ab initio calculations. The agreement between the ab initio and fitted data for the ground state is better than 0.1%, while for the two excited states the agreement is 1% and 11% for the Ae and Be constants, respectively.
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A. Zenesini, B. Huang, M. Berninger, S. Besler, H. Nägerl, F. Ferlaino, R. Grimm, C. Greene, J. von Stecher Resonant five-body recombination in an ultracold gas of bosonic atoms,
New J. Phys. 15 043040 (2013-04-22),
http://dx.doi.org/10.1088/1367-2630/15/4/043040 doi:10.1088/1367-2630/15/4/043040 (ID: 718073)
Toggle Abstract
We combine theory and experiment to investigate five-body recombination in an ultracold gas of atomic cesium at negative scattering length. A refined theoretical model, in combination with extensive laboratory tunability of the interatomic interactions, enables the five-body resonant recombination rate to be calculated and measured. The position of the new observed recombination feature agrees with a recent theoretical prediction and supports the prediction of a family of universal cluster states at negative a that are tied to an Efimov trimer.
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M. Berninger, A. Zenesini, B. Huang, W. Harm, H. Nägerl, F. Ferlaino, R. Grimm, P. S. Julienne, J. M. Hutson Feshbach resonances, weakly bound molecular states, and coupled-channel potentials for cesium at high magnetic fields,
Phys. Rev. A 87 032517 (2013-03-25),
http://dx.doi.org/10.1103/PhysRevA.87.032517 doi:10.1103/PhysRevA.87.032517 (ID: 718341)
Toggle Abstract
We explore the scattering properties of ultracold ground-state Cs atoms at magnetic fields between 450 G (45 mT) and 1000 G. We identify 17 new Feshbach resonances, including two very broad ones near 549 G and 787 G. We measure the binding energies of several different dimer states by magnetic field modulation spectroscopy. We use least-squares fitting to these experimental results, together with previous measurements at lower field, to determine a new 6-parameter model of the long-range interaction potential, designated M2012. Coupled-channels calculations using M2012 provide an accurate mapping between the s-wave scattering length and the magnetic field over the entire range of fields considered. This mapping is crucial for experiments that rely on precise tuning of the scattering length, such as those on Efimov physics.
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K. Aikawa, A. Frisch, M. Mark, S. Baier, A. Rietzler, R. Grimm, F. Ferlaino Bose-Einstein Condensation of Erbium,
Phys. Rev. Lett. 108 210401 (2012-05-21),
http://dx.doi.org/10.1103/PhysRevLett.108.210401 doi:10.1103/PhysRevLett.108.210401 (ID: 718048)
Toggle Abstract
We report on the achievement of Bose-Einstein condensation of erbium atoms and on the observation of
magnetic Feshbach resonances at low magnetic field. By means of evaporative cooling in an optical dipole
trap, we produce pure condensates of 168Er, containing up to 7×104 atoms. Feshbach spectroscopy reveals
an extraordinary rich loss spectrum with six loss resonances already in a narrow magnetic-field range up to
3 G. Finally, we demonstrate the application of a low-field Feshbach resonance to produce a tunable dipolar
Bose-Einstein condensate and we observe its characteristic d-wave collapse.
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A. Frisch, K. Aikawa, M. Mark, A. Rietzler, J. Schindler, E. Zupanic, R. Grimm, F. Ferlaino Narrow-line magneto-optical trap for erbium: Simple approach for a complex atom,
Phys. Rev. A 85 051401 (2012-05-07),
http://dx.doi.org/10.1103/PhysRevA.85.051401 doi:10.1103/PhysRevA.85.051401 (ID: 718027)
Toggle Abstract
We report on the experimental realization of a robust and efficient magneto-optical trap for erbium atoms, based on a narrow cooling transition at 583 nm. We observe up to N=2×108 atoms at a temperature of about T=15 μK. This simple scheme provides better starting conditions for direct loading of dipole traps as compared to approaches based on the strong cooling transition alone, or on a combination of a strong and a narrow kHz transition. Our results on Er point to a general, simple, and efficient approach to laser cool samples of other lanthanide atoms (Ho, Dy, and Tm) for the production of quantum-degenerate samples.
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T. Takekoshi, M. Debatin, R. Rameshan, F. Ferlaino, R. Grimm, H. Nägerl, C. Le Sueur, J. M. Hutson, P. S. Julienne, S. Kotochigova, E. Tiemann Towards the production of ultracold ground-state RbCs molecules: Feshbach resonances, weakly bound states, and the coupled-channel model,
Phys. Rev. A 85 032506 (2012-03-05),
http://dx.doi.org/10.1103/PhysRevA.85.032506 doi:10.1103/PhysRevA.85.032506 (ID: 718010)
Toggle Abstract
We have studied interspecies scattering in an ultracold mixture of 87Rb and 133Cs atoms, both in their lowest-energy spin states. The three-body loss signatures of 30 incoming s- and p-wave magnetic Feshbach resonances over the range 0 to 667 G have been cataloged. Magnetic field modulation spectroscopy was used to observe molecular states bound by up to 2.5 MHz×h. We have created RbCs Feshbach molecules using two of the resonances. Magnetic moment spectroscopy along the magnetoassociation pathway from 197 to 182 G gives results consistent with the observed and calculated dependence of the binding energy on magnetic field strength. We have set up a coupled-channel model of the interaction and have used direct least-squares fitting to refine its parameters to fit the experimental results from the Feshbach molecules, in addition to the Feshbach resonance positions and the spectroscopic results for deeply bound levels. The final model gives a good description of all the experimental results and predicts a large resonance near 790 G, which may be useful for tuning the interspecies scattering properties. Quantum numbers and vibrational wave functions from the model can also be used to choose optimal initial states of Feshbach molecules for their transfer to the rovibronic ground state using stimulated Raman adiabatic passage.
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F. Ferlaino, A. Zenesini, M. Berninger, B. Huang, H. C. Nägerl, R. Grimm Efimov Resonances in Ultracold Quantum Gases,
Few-Body Syst. 51 133 (2011-10-09),
http://dx.doi.org/10.1007/s00601-011-0260-7 doi:10.1007/s00601-011-0260-7 (ID: 717751)
Toggle Abstract
Ultracold atomic gases have developed into prime systems for experimental studies of Efimov three-body physics and related few-body phenomena, which occur in the universal regime of resonant interactions. In the last few years, many important breakthroughs have been achieved, confirming basic predictions of universal few-body theory and deepening our understanding of such systems. We review the basic ideas along with the fast experimental developments of the field, focussing on ultracold cesium gases as a well-investigated model system. Triatomic Efimov resonances, atom-dimer Efimov resonances, and related four-body resonances are discussed as central observables. We also present some new observations of such resonances, supporting and complementing the set of available data.
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M. Debatin, T. Takekoshi, R. Rameshan, L. Reichsöllner, F. Ferlaino, R. Grimm, R. Vexiau, N. Bouloufa, O. Dulieu, H. C. Nägerl Molecular spectroscopy for ground-state transfer of ultracold RbCs molecules,
Phys. Chem. Chem. Phys. 13 18935 (2011-07-24),
http://dx.doi.org/10.1039/C1CP21769K doi:10.1039/C1CP21769K (ID: 717719)
Toggle Abstract
We perform one- and two-photon high resolution spectroscopy on ultracold samples of RbCs Feshbach molecules with the aim to identify a suitable route for efficient ground-state transfer in the quantum-gas regime to produce quantum gases of dipolar RbCs ground-state molecules. One-photon loss spectroscopy allows us to probe deeply bound rovibrational levels of the mixed excited (A1{\Sigma}+ - b3{\Pi}0) 0+ molecular states. Two-photon dark state spectroscopy connects the initial Feshbach state to the rovibronic ground state. We determine the binding energy of the lowest rovibrational level |v"=0,J"=0> of the X1{\Sigma}+ ground state to be DX 0 = 3811.5755(16) 1/cm, a 300-fold improvement in accuracy with respect to previous data. We are now in the position to perform stimulated two-photon Raman transfer to the rovibronic ground state.
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M. Berninger, A. Zenesini, B. Huang, W. Harm, H. C. Nägerl, F. Ferlaino, R. Grimm, P. S. Julienne, J. M. Hutson Universality of the Three-Body Parameter for Efimov States in Ultracold Cesium,
Phys. Rev. Lett. 107 120401 (2011-06-20),
http://dx.doi.org/10.1103/PhysRevLett.107.120401 doi:10.1103/PhysRevLett.107.120401 (ID: 717706)
Toggle Abstract
We report on the observation of triatomic Efimov resonances in an ultracold gas of cesium atoms. Exploiting the wide tunability of interactions resulting from three broad Feshbach resonances in the same spin channel, we measure magnetic-field dependent three-body recombination loss. The positions of the loss resonances yield corresponding values for the three-body parameter, which in universal few-body physics is required to describe three-body phenomena and in particular to fix the spectrum of Efimov states. Our observations show a robust universal behavior with a three-body parameter that stays essentially constant.
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A. Lercher, T. Takekoshi, M. Debatin, B. Schuster, R. Rameshan, F. Ferlaino, R. Grimm, H. C. Nägerl Production of a dual-species Bose-Einstein condensate of Rb and Cs atoms,
Eur. Phys. J. D 65 9 (2011-03-25),
http://dx.doi.org/10.1140/epjd/e2011-20015-6 doi:10.1140/epjd/e2011-20015-6 (ID: 717717)
Toggle Abstract
We report the simultaneous production of Bose-Einstein condensates (BECs) of and atoms in separate optical traps. The two samples are mixed during laser cooling and loading but are separated by 400 μm for the final stage of evaporative cooling. This is done to avoid considerable interspecies three-body recombination, which causes heating and evaporative loss. We characterize the BEC production process, discuss limitations, and outline the use of the dual-species BEC in future experiments to produce rovibronic ground state molecules, including a scheme facilitated by the superfluid-to-Mott-insulator (SF-MI) phase transition.
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S. Knoop, F. Ferlaino, M. Berninger, M. Mark, H. Nägerl, R. Grimm, J. P. D'Incao, B. Esry Magnetically Controlled Exchange Process in an Ultracold Atom-Dimer Mixture,
Phys. Rev. Lett. 104 053201 (2009-11-10),
http://dx.doi.org/10.1103/PhysRevLett.104.053201 doi:10.1103/PhysRevLett.104.053201 (ID: 717092)
Toggle Abstract
We report on the observation of an elementary exchange process in an optically trapped ultracold sample of atoms and Feshbach molecules. We can magnetically control the energetic nature of the process and tune it from endoergic to exoergic, enabling the observation of a pronounced threshold behavior. In contrast to relaxation to more deeply bound molecular states, the exchange process does not lead to trap loss. We find excellent agreement between our experimental observations and calculations based on the solutions of three-body Schr\"odinger equation in the adiabatic hyperspherical representation. The high efficiency of the exchange process is explained by the halo character of both the initial and final molecular states.
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K. Pilch, A. D. Lange, A. Prantner, G. Kerner, F. Ferlaino, H. Nägerl, R. Grimm Observation of interspecies Feshbach resonances in an ultracold Rb-Cs mixture,
Phys. Rev. A 79 042718 (2009-04-30),
http://dx.doi.org/10.1103/PhysRevA.79.042718 doi:10.1103/PhysRevA.79.042718 (ID: 660704)
Toggle Abstract
We report on the observation of interspecies Feshbach resonances in an ultracold, optically trapped mixture of Rb and Cs atoms. In a magnetic field range up to 300 G we find 23 interspecies Feshbach resonances in the lowest spin channel and 2 resonances in a higher channel of the mixture. The extraordinarily rich Feshbach spectrum suggests the importance of different partial waves in both the open and closed channels of the scattering problem along with higher-order coupling mechanisms. Our results provide, on one hand, fundamental experimental input to characterize the Rb-Cs scattering properties and, on the other hand, identify possible starting points for the association of ultracold heteronuclear RbCs molecules.
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F. Ferlaino, S. Knoop, M. Berninger, W. Harm, J. P. D'Incao, H. Nägerl, R. Grimm Evidence for universal four-body states tied to an Efimov trimer,
Phys. Rev. Lett. 102 140401 (2009-04-09),
http://dx.doi.org/10.1103/PhysRevLett.102.140401 doi:10.1103/PhysRevLett.102.140401 (ID: 717103)
Toggle Abstract
We report on the measurement of four-body recombination rate coefficients in an atomic gas. Our results obtained with an ultracold sample of cesium atoms at negative scattering lengths show a resonant enhancement of losses and provide strong evidence for the existence of a pair of four-body states, which is strictly connected to Efimov trimers via universal relations. Our findings confirm recent theoretical predictions and demonstrate the enrichment of the Efimov scenario when a fourth particle is added to the generic three-body problem.
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S. Knoop, F. Ferlaino, M. Mark, M. Berninger, H. Schöbel, H. Nägerl, R. Grimm Observation of an Efimov-like trimer resonance in ultracold atom-dimer scattering,
Nature Phys. 5 227-230 (2009-02-09),
http://dx.doi.org/10.1038/nphys1203 doi:10.1038/nphys1203 (ID: 717105)
Toggle Abstract
The field of few-body physics has originally been motivated by understanding nuclear matter. New model systems to experimentally explore few-body quantum systems can now be realized in ultracold gases with tunable interactions. Albeit the vastly different energy regimes of ultracold and nuclear matter (peV as compared to MeV), few-body phenomena are universal for near-resonant two-body interactions. Efimov states represent a paradigm for universal three-body states, and evidence for their existence has been obtained in measurements of three-body recombination in an ultracold gas of caesium atoms. Interacting samples of halo dimers can provide further information on universal few-body phenomena. Here we study interactions in an optically trapped mixture of such halo dimers with atoms, realized in a caesium gas at nanokelvin temperatures. We observe an atom-dimer scattering resonance, which we interpret as being due to a trimer state hitting the atom-dimer threshold. We discuss the close relation of this observation to Efimov's scenario, and in particular to atom-dimer Efimov resonances.
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A. D. Lange, K. Pilch, A. Prantner, F. Ferlaino, B. Engeser, H. Nägerl, R. Grimm, C. Chin Determination of atomic scattering lengths from measurements of molecular binding energies near Feshbach resonances,
Phys. Rev. A 79 013622 (2009-01-23),
http://dx.doi.org/10.1103/PhysRevA.79.013622 doi:10.1103/PhysRevA.79.013622 (ID: 660710)
Toggle Abstract
We present an analytic model to calculate the atomic scattering length near a Feshbach resonance from data on the molecular binding energy. Our approach considers finite-range square-well potentials and can be applied near broad, narrow, or even overlapping Feshbach resonances. We test our model on Cs2 Feshbach molecules. We measure the binding energy using magnetic-field modulation spectroscopy in a range where one broad and two narrow Feshbach resonances overlap. From the data we accurately determine the Cs atomic scattering length and the positions and widths of two particular resonances.
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