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K. Vodenkova, A. Pocklington, F. Yang, A. Lingenfelter, A. A. Clerk, H. Pichler Efficient Simulation of Nonreciprocal Many-body Physics via Quantum Feedback,
(2026-09-02),
arXiv:2609.02518 arXiv:2609.02518
We present a scheme to efficiently simulate nonreciprocal many-body spin models using a non-Markovian open system. Our scheme utilizes a single quantum emitter coupled to a waveguide mode that is fed back to the same emitter after a time delay. With this coherent delayed feedback, an effective nonreciprocal interaction can be engineered, wherein the emitter at earlier times affects itself at later times, creating a scalable spin chain. We show that all the steady-state quantities of such spin models can be accessed through measurement of the emitter and the output field. Furthermore, using classical feedback that resets the emitter, quench dynamics from arbitrary product states can be simulated. We demonstrate striking features of nonreciprocal models, such as the Liouvillian skin effect, anomalous relaxation dynamics, and quasi-long-range order of output photons. Finally, we show that the proposal is amenable to experimental realization and robust to imperfections. Our work establishes a feasible way to scale up a nonreciprocal many-body system, and provides a new route towards generation of exotic states of light.
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G. Calliari, C. Fromonteil, F. Cesa, T. Zache, P. M. Preiss, R. Ott, H. Pichler Programmable Fermionic Quantum Processors with Globally Controlled Lattices,
(2026-04-14),
arXiv:2604.13160 arXiv:2604.13160
We introduce a framework for realizing universal fermionic quantum processing with globally controlled itinerant fermionic particles. Our approach is tailored to the example of neutral atoms in optical lattices, but transposes to other setups with similar capabilities. We give constructive protocols to realize arbitrary fermionic processes, with time-dependent control over global parameters of the experimental setup, such as tunneling and interaction in a Fermi-Hubbard type model. We first prove the universality of our framework and then discuss implementation variants, such as hybrid analog-digital simulation of extended Fermi-Hubbard models, e.g., with long-range couplings.
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L. Bombieri, T. Zache, H. Pichler, D. Gonzalez Cuadra U(1) lattice gauge theory and string roughening on a triangular Rydberg array,
(2026-02-05),
arXiv:2602.06123 arXiv:2602.06123
Lattice gauge theories (LGTs) describe fundamental interactions in particle physics. A central phenomenon in these theories is confinement, which binds quarks and antiquarks into hadrons through the formation of string-like flux tubes of gauge fields. Simulating confinement dynamics is a challenging task, but recent advances in quantum simulation are enabling the exploration of LGTs in regimes beyond the reach of classical computation. For analog devices, a major difficulty is the realization of strong plaquette interactions, which generate string fluctuations that can drive a roughening transition. Understanding string roughening -- where strong transversal functions lead to an effective restoration of translational symmetry at long distances -- is of central importance in the study of confinement. In this work, we show that string roughening emerges naturally in an analog Rydberg quantum simulator. We first map a triangular Rydberg array onto a (2+1)D U(1) LGT where plaquette terms appear as first-order processes. We study flux strings connecting static charges and demonstrate that, near a deconfined quantum critical point, the string exhibits logarithmic growth of its transverse width as the separation between charges increases, along with the universal Lüscher correction to the confining potential -- both signatures of string roughening. Finally, we investigate the real-time dynamics of an initially rigid string, observing large fluctuations after quenching into the roughening regime, as well as string breaking via particle-pair creation. Our results indicate that rough strings can be realized in experimentally accessible quantum simulators, opening the door to detailed studies of how strong fluctuations influence string-breaking dynamics.
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F. Cesa, A. Di Fini, D. A. Korbany, R. Tricarico, H. Bernien, H. Pichler, L. Piroli Engineering discrete local dynamics in globally driven dual-species atom arrays,
(2026-01-23),
arXiv:2601.16961 arXiv:2601.16961
We introduce a method for engineering discrete local dynamics in globally-driven dual-species neutral atom experiments, allowing us to study emergent digital models through uniform analog controls. Leveraging the new opportunities offered by dual-species systems, such as species-alternated driving, our construction exploits simple Floquet protocols on static atom arrangements, and benefits of generalized blockade regimes (different inter- and intra-species interactions). We focus on discrete dynamical models that are special examples of Quantum Cellular Automata (QCA), and explicitly consider a number of relevant examples, including the kicked-Ising model, the Floquet Kitaev honeycomb model, and the digitization of generic translation-invariant nearest-neighbor Hamiltonians (e.g., for Trotterized evolution). As an application, we study chaotic features of discretized many-body dynamics that can be detected by leveraging only demonstrated capabilities of globally-driven experiments, and benchmark their ability to discriminate chaotic evolution.
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R. P. White, V. Ramesh, A. Impertro, S. Anand, F. Cesa, G. Giudici, T. Iadecola, H. Pichler, H. Bernien Quantum Cellular Automata on a Dual-Species Rydberg Processor,
(2026-01-22),
arXiv:2601.16257 arXiv:2601.16257
As quantum devices scale to larger and larger sizes, a significant challenge emerges in scaling their coherent controls accordingly. Quantum cellular automata (QCAs) constitute a promising framework that bypasses this control problem: universal dynamics can be achieved using only a static qubit array and global control operations. Despite an extensive history of theoretical explorations and proposals, QCAs have not been experimentally explored in the context of highly-scalable globally-controlled systems. Here we realize QCAs on a dual-species Rydberg array of rubidium and cesium atoms, leveraging independent global control of each species to perform multiple quantum protocols. Seeding an automaton with different initial states, we explore many-body dynamics of quasiparticles and grow GHZ states across both species, highlighting the flexibility of our approach. We further develop a second automaton using a novel mediated entangling gate, enabling generation of 96.7(1.7)\%-fidelity Bell states, 17-qubit cluster states, and high-connectivity graph states. Our results demonstrate that simple global controls enable access to a rich variety of applications through the QCA framework. The versatility and scalability of QCAs present compelling opportunities for the development of quantum information systems, as well as new perspectives on quantum many-body dynamics.
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R. White, V. Ramesh, A. Impertro, S. Anand, F. Cesa, G. Giudici, T. Iadecola, H. Pichler, H. Bernien Quantum Cellular Automata on a Dual-Species Rydberg Processor,
(2026-01-22),
arXiv:2601.16257 arXiv:2601.16257
As quantum devices scale to larger and larger sizes, a significant challenge emerges in scaling their coherent controls accordingly. Quantum cellular automata (QCAs) constitute a promising framework that bypasses this control problem: universal dynamics can be achieved using only a static qubit array and global control operations. We realize QCAs on a dual-species Rydberg array of rubidium and cesium atoms, leveraging independent global control of each species to perform a myriad of quantum protocols. With simple pulse sequences, we explore many-body dynamics and generate a variety of entangled states, including GHZ states, 96.7(1.7)\\%-fidelity Bell states, 17-qubit cluster states, and high-connectivity graph states. The versatility and scalability of QCAs offers compelling routes for scaling quantum information systems with global controls, as well as new perspectives on quantum many-body dynamics.
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R. Ott, T. Zache, S. Choi, A. Kaufman, H. Pichler Rare-Event Quantum Sensing using Logical Qubits,
(2026-01-07),
arXiv:2601.04313 arXiv:2601.04313
bert Ott, Torsten V. Zache, Soonwon Choi, Adam M. Kaufman, Hannes Pichler<br /><br />
<br /><br />
We present a novel protocol to detect rare signals in a noisy environment using quantum error correction (QEC). The key feature of our protocol is the discrimination between signal and noise through distinct higher-order correlations, realized by the non-linear processing that occurs during syndrome extraction in QEC. In this scheme, QEC has two effects: First, it sacrifices part of the signal by recording a reduced, stochastic, logical phase . Second, it corrects the physical noise and extends the (logical) coherence time for signal acquisition. For rare signals occurring at random times in the presence of local Markovian noise, we explicitly demonstrate an improved sensitivity of our approach over more conventional sensing strategies.
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L. Bombieri, T. Zache, G. Calliari, M. Lukin, H. Pichler, D. Gonzalez Cuadra Deconfined quantum criticality on a triangular Rydberg array,
Phys. Rev. Lett. 135 233602 (2025-12-04),
http://dx.doi.org/10.1103/4rg4-zbnn doi:10.1103/4rg4-zbnn
Fluctuations can drive continuous phase transitions between two distinct ordered phases -- so-called Deconfined Quantum Critical points (DQCPs) -- which lie beyond the Landau-Ginzburg-Wilson paradigm. Despite several theoretical predictions over the past decades, experimental evidence of DQCPs remains elusive. We show that a DQCP can be explored in a system of Rydberg atoms arranged on a triangular lattice and coupled through van der Waals interactions. Specifically, we investigate the nature of the phase transition between two ordered phases at 1/3 and at 2/3 Rydberg excitation density, which were recently probed experimentally in [P. Scholl et al., Nature 595, 233 (2021)]. Using a field-theoretical analysis, we predict both the critical exponents for infinitely long cylinders of increasing circumference and the emergence of a conformal field theory near criticality showing an enlarged U(1) symmetry -- a signature of DQCPs -- and confirm these predictions numerically. Finally, we extend these results to ladder geometries and show how the emergent U(1) symmetry could be probed experimentally using finite tweezer arrays.
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A. Warman, F. Yang, A. Tiwari, H. Pichler, S. Schafer-Nameki Categorical Symmetries in Spin Models with Atom Arrays,
Phys. Rev. Lett. 135 206503 (2025-11-13),
http://dx.doi.org/10.1103/249m-m8wq doi:10.1103/249m-m8wq
Categorical symmetries have recently been shown to generalize the classification of phases of matter, significantly broadening the traditional Landau paradigm. To test these predictions, we propose a simple spin chain model that encompasses all gapped phases and second-order phase transitions governed by the categorical symmetry ????????????(????8)
. This model not only captures the essential features of noninvertible phases but is also straightforward enough to enable practical realization. Specifically, we outline an implementation using neutral atoms trapped in optical tweezer arrays. Employing a dual-species setup and Rydberg blockade, we propose a digital simulation approach that can efficiently implement the many-body evolution in several nontrivial quantum phases.
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R. Ott, T. Zache, N. Maskara, M. Lukin, P. Zoller, H. Pichler Probing topological entanglement on large scales,
Phys. Rev. Lett. 135 90401 (2025-08-25),
http://dx.doi.org/10.1103/mdsf-wrbj doi:10.1103/mdsf-wrbj
Topologically ordered quantum matter exhibits intriguing long-range patterns of entanglement, which reveal themselves in subsystem entropies. However, measuring such entropies, which can be used to certify topological order, on large partitions is challenging and becomes practically unfeasible for large systems. We propose a protocol based on local adiabatic deformations of the Hamiltonian which extracts the universal features of long-range topological entanglement from measurements on small subsystems of finite size, trading an exponential number of measurements against a polynomial-time evolution. Our protocol is general and readily applicable to various quantum simulation architectures. We apply our method to various string-net models representing both abelian and non-abelian topologically ordered phases, and illustrate its application to neutral atom tweezer arrays with numerical simulations.
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R. Ott, D. González-Cuadra, T. Zache, P. Zoller, A. Kaufman, H. Pichler Error-corrected fermionic quantum processors with neutral atoms,
Phys. Rev. Lett. 135 90601 (2025-08-25),
http://dx.doi.org/10.1103/zkpl-hh28 doi:10.1103/zkpl-hh28
Many-body fermionic systems can be simulated in a hardware-efficient manner using a fermionic quantum processor. Neutral atoms trapped in optical potentials can realize such processors, where non-local fermionic statistics are guaranteed at the hardware level. Implementing quantum error correction in this setup is however challenging, due to the atom-number superselection present in atomic systems, that is, the impossibility of creating coherent superpositions of different particle numbers. In this work, we overcome this constraint and present a blueprint for an error-corrected fermionic quantum computer that can be implemented using current experimental capabilities. To achieve this, we first consider an ancillary set of fermionic modes and design a fermionic reference, which we then use to construct superpositions of different numbers of referenced fermions. This allows us to build logical fermionic modes that can be error corrected using standard atomic operations. Here, we focus on phase errors, which we expect to be a dominant source of errors in neutral-atom quantum processors. We then construct logical fermionic gates, and show their implementation for the logical particle-number conserving processes relevant for quantum simulation. Finally, our protocol is illustrated using a minimal fermionic circuit, where it leads to a quadratic suppression of the logical error rate.
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P. Grochowski, H. Pichler, C. A. Regal, O. Romero-Isart Quantum control of continuous systems via nonharmonic potential modulation,
Quantum 9 1824 (2025-08-08),
http://dx.doi.org/10.22331/q-2025-08-08-1824 doi:10.22331/q-2025-08-08-1824
We present a theoretical proposal for preparing and manipulating a state of a single continuous-variable degree of freedom confined to a nonharmonic potential. By utilizing optimally controlled modulation of the potential's position and depth, we demonstrate the generation of non-Gaussian states, including Fock, Gottesman-Kitaev-Preskill, multi-legged-cat, and cubic-phase states, as well as the implementation of arbitrary unitaries within a selected two-level subspace. Additionally, we propose protocols for single-shot orthogonal state discrimination and algorithmic cooling and analyze the robustness of this control scheme against noise. Since all the presented protocols rely solely on the precise modulation of the effective nonharmonic potential landscape, they are relevant to several experiments with continuous-variable systems, including the motion of a single particle in an optical tweezer or lattice, or current in circuit quantum electrodynamics.
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G. Giudici, S. Veroni, G. Giudice, H. Pichler, J. Zeiher Fast entangling gates for Rydberg atoms via resonant dipole-dipole interaction,
PRX Quantum 6 30308 (2025-07-17),
http://dx.doi.org/10.1103/5d8p-3hm1 doi:10.1103/5d8p-3hm1
The advent of digital neutral-atom quantum computers relies on the development of fast and robust protocols for high-fidelity quantum operations. In this work, we introduce a novel scheme for entangling gates using four atomic levels per atom: a ground state qubit and two Rydberg states. A laser field couples the qubit to one of the two Rydberg states, while a microwave field coupling the two Rydberg states enables a resonant dipole-dipole interaction between different atoms. We show that this interaction can mediate controlled-Z gates that are faster and less sensitive to Rydberg decay than state-of-the-art Rydberg gates based on van der Waals interactions. Moreover, we systematically stabilize our protocol against interatomic distance fluctuations and analyze its performance in realistic setups with rubidium or cesium atoms. Our results open up new avenues to the use of dipolar interactions for universal quantum computation with neutral atoms.
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G. Calliari, M. Di Liberto, H. Pichler, T. Zache Quantum simulating continuum field theories with large-spin lattice models,
PRX Quantum 6 30304 (2025-07-09),
http://dx.doi.org/10.1103/nt76-ttmj doi:10.1103/nt76-ttmj
Simulating the real-time dynamics of quantum field theories (QFTs) is one of the most promising applications of quantum simulators. Regularizing a bosonic QFT for quantum simulation purposes typically involves a truncation in Hilbert space in addition to a discretization of space. Here, we discuss how to perform such a regularization of scalar QFTs using multi-level or qudit systems, and show that this enables quantitative predictions in the continuum limit by extrapolating results obtained for large-spin lattice models. With extensive matrix-product state simulations, we numerically demonstrate the sequence of extrapolations that leads to quantitative agreement of observables for the integrable sine-Gordon (sG) QFT. We further show how to prepare static and moving soliton excitations, and analyze their scattering dynamics, in agreement with a semi-classical model and analytical predictions. Finally, we illustrate how a non-integrable perturbation of the sG model gives rise to dynamics reminiscent of string breaking and plasma oscillations in gauge theories. Our methods are directly applicable in state-of-the-art analog quantum simulators, opening the door to implementing a wide variety of scalar field theories and tackling long-standing questions in non-equilibrium QFT like the fate of the false vacuum.
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L. Bombieri, Z. Zeng, R. Tricarico, R. Lin, S. Notarnicola, M. Cain, M. Lukin, H. Pichler Quantum adiabatic optimization with Rydberg arrays: localization phenomena and encoding strategies,
PRX Quantum 6 20306 (2025-04-08),
http://dx.doi.org/10.1103/PRXQuantum.6.020306 doi:10.1103/PRXQuantum.6.020306
We study the quantum dynamics of the encoding scheme proposed in [Nguyen et al., PRX Quantum 4, 010316 (2023)], which encodes optimization problems on graphs with arbitrary connectivity into Rydberg atom arrays. Here, a graph vertex is represented by a wire of atoms, and the (crossing) crossing-with-edge gadget is placed at the intersection of two wires to (de)couple their degrees of freedom and reproduce the graph connectivity. We consider the fundamental geometry of two vertex-wires intersecting via a single gadget and look at minimum gap scaling with system size along adiabatic protocols. We find that both polynomial and exponential scaling are possible and, by means of perturbation theory, we relate the exponential closing of the minimum gap to an unfavorable localization of the ground-state wavefunction. Then, on the QuEra Aquila neutral atom machine, we observe such localization and its effect on the success probability of finding the correct solution to the encoded optimization problem. Finally, we propose possible strategies to avoid this quantum bottleneck, leading to an exponential improvement in the adiabatic performance.
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Z. Zeng, G. Giudici, H. Pichler Quantum dimer models with Rydberg gadgets,
Phys. Rev. Research 7 L012006 (2025-01-09),
http://dx.doi.org/10.1103/PhysRevResearch.7.L012006 doi:10.1103/PhysRevResearch.7.L012006
The Rydberg blockade mechanism is an important ingredient in quantum simulators based on neutral atom arrays. It enables the emergence of a rich variety of quantum phases of matter, such as topological spin liquids. The typically isotropic nature of the blockade effect, however, restricts the range of natively accessible models and quantum states. In this work, we propose a method to systematically overcome this limitation, by developing gadgets, i.e., specific arrangements of atoms, that transform the underlying Rydberg blockade into more general constraints. We apply this technique to realize dimer models on square and triangular geometries. In these setups, we study the role of the quantum fluctuations induced by a coherent drive of the atoms and find signatures of U(1) and Z2 quantum spin liquid states in the respective ground states. Finally, we show that these states can be dynamically prepared with high fidelity, paving the way for the quantum simulation of a broader class of constrained models and topological matter in experiments with Rydberg atom arrays.
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C. Fromonteil, D. Vasilyev, T. Zache, K. Hammerer, A. M. Rey, J. Ye, H. Pichler, P. Zoller Non-local mass superpositions and optical clock interferometry in atomic ensemble quantum networks,
(2025-09-23),
arXiv:2509.19501 arXiv:2509.19501
Quantum networks are emerging as powerful platforms for sensing, communication, and fundamental tests of physics. We propose a programmable quantum sensing network based on entangled atomic ensembles, where optical clock qubits emulate mass superpositions in atom and atom-clock interferometry. Our approach uniquely combines scalability to large atom numbers with minimal control requirements, relying only on collective addressing of internal atomic states. This enables the creation of both non-local and local superpositions with spatial separations beyond those achievable in conventional interferometry. Starting from Bell-type seed states distributed via photonic channels, collective operations within atomic ensembles coherently build many-body mass superpositions sensitive to gravitational redshift. The resulting architecture realizes a non-local Ramsey interferometer, with gravitationally induced phase shifts observable in network-based interference patterns. Beyond extending the spatial reach of mass superpositions, our scheme establishes a scalable, programmable platform to probe the interface of quantum mechanics and gravity, and offers a new experimental pathway to test atom and atom-clock interferometer proposals in a network-based quantum laboratory.
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T. Vovk, A. Van de Walle, H. Pichler, A. Bohrdt Neural quantum states for emitter dynamics in waveguide QED,
(2025-08-12),
arXiv:2508.08964 arXiv:2508.08964
Quantum emitters coupled to one-dimensional waveguides constitute a paradigmatic quantum-optical platform for exploring collective phenomena in open quantum many-body systems. For appropriately spaced emitters, they realize the Dicke model, whose characteristic permutation symmetry allows for efficient exact solutions featuring superradiance. When the emitters are arbitrarily spaced, however, this symmetry is lost and general analytical solutions are no longer available. In this work, we introduce a novel numerical method to study the dynamics of such systems by extending the time-dependent neural quantum state (t-NQS) framework to open quantum systems. We benchmark our approach across a range of waveguide QED settings and compare its performance with tensor-network calculations. Our results demonstrate that the t-NQS approach is competitive with other numerical methods and highlight the potential of t-NQSs for studying open quantum many-body systems out of equilibrium.
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G. Calliari, R. Ott, H. Pichler, T. Zache Field digitization scaling in a Z symmetric model,
(2025-07-30),
arXiv:2507.22984 arXiv:2507.22984
The simulation of quantum field theories, both classical and quantum, requires regularization of infinitely many degrees of freedom. However, in the context of field digitization (FD) -- a truncation of the local fields to discrete values -- a comprehensive framework to obtain continuum results is currently missing. Here, we propose to analyze FD by interpreting the parameter as a coupling in the renormalization group (RG) sense. As a first example, we investigate the two-dimensional classical -state clock model as a Z FD of the -symmetric -model. Using effective field theory, we employ the RG to derive generalized scaling hypotheses involving the FD parameter , which allows us to relate data obtained for different -regularized models in a procedure that we term (FDS). Using numerical tensor-network calculations at finite bond dimension , we further uncover an unconventional universal crossover around a low-temperature phase transition induced by finite , demonstrating that FDS can be extended to describe the interplay of and . Finally, we analytically prove that our calculations for the 2D classical-statistical Z clock model are directly related to the quantum physics in the ground state of a (2+1)D Z lattice gauge theory which serves as a FD of compact quantum electrodynamics. Our study thus paves the way for applications of FDS to quantum simulations of more complex models in higher spatial dimensions, where it could serve as a tool to analyze the continuum limit of digitized quantum field theories.
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A. Senoo, A. Baumgärtner, J. W. Lis, G. M. Vaidya, Z. Zeng, G. Giudici, H. Pichler, A. Kaufman High-fidelity entanglement and coherent multi-qubit mapping in an atom array,
(2025-06-16),
arXiv:2506.13632 arXiv:2506.13632
Neutral atoms in optical tweezer arrays possess broad applicability for quantum information science, in computing, simulation, and metrology. Among atomic species, Ytterbium-171 is unique as it hosts multiple qubits, each of which is impactful for these distinct applications. Consequently, this atom is an ideal candidate to bridge multiple disciplines, which, more broadly, has been an increasingly effective strategy within the field of quantum science. Realizing the full potential of this synergy requires high-fidelity generation and transfer of many-particle entanglement between these distinct qubit degrees of freedom, and thus between these distinct applications. Here we demonstrate the creation and coherent mapping of entangled quantum states across multiple qubits in Ytterbium-171 tweezer arrays. We map entangled states onto the optical clock qubit from the nuclear spin qubit or the Rydberg qubit. We coherently transfer up to 20 atoms of a -ordered Greenberger-Horne-Zeilinger (GHZ) state from the interacting Rydberg manifold to the metastable nuclear spin manifold. The many-body state is generated via a novel disorder-robust pulse in a two-dimensional ladder geometry. We further find that clock-qubit-based spin detection applied to Rydberg and nuclear spin qubits facilitates atom-loss-detectable qubit measurements and Rydberg decay detection. This enables mid-circuit and delayed erasure detection, yielding an error-detected two-qubit gate fidelity of in the metastable qubits as well as enhanced GHZ state fidelities in analog preparation. These results establish a versatile architecture that advances multiple fields of quantum information science while also establishing bridges between them.
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F. Cesa, H. Bernien, H. Pichler Fast and Error-Correctable Quantum RAM,
(2025-03-24),
arXiv:2503.19172v1 arXiv:2503.19172v1
Quantum devices can process data in a fundamentally different way than classical computers. To leverage this potential, many algorithms require the aid of a quantum Random Access Memory (QRAM), i.e. a module capable of efficiently loading datasets (both classical and quantum) onto the quantum processor. However, a realization of this fundamental building block is still outstanding, since existing proposals require prohibitively many resources for reliable implementations, or are not compatible with current architectures. Moreover, present approaches cannot be scaled-up, as they do not allow for efficient quantum error-correction. Here we develop a QRAM design, that enables fast and robust QRAM calls, naturally allows for fault-tolerant and error-corrected operation, and can be integrated on present hardware. Our proposal employs a special quantum resource state that is consumed during the QRAM call: we discuss how it can be assembled and processed efficiently in a dedicated module, and give detailed blueprints for modern neutral-atom processors. Our work places a long missing, fundamental component of quantum computers within reach of currently available technology; this opens the door to algorithms featuring practical quantum advantage, including search or oracular problems, quantum chemistry and machine learning.
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R. Ott, T. Zache, M. Prüfer, S. Erne, M. Tajik, H. Pichler, J. Schmiedmayer, P. Zoller Hamiltonian Learning in Quantum Field Theories,
Phys. Rev. Research 6 43284 (2024-12-16),
http://dx.doi.org/10.1103/PhysRevResearch.6.043284 doi:10.1103/PhysRevResearch.6.043284
We discuss Hamiltonian learning in quantum field theories as a protocol for systematically extracting the operator content and coupling constants of effective field theory Hamiltonians from experimental data. Learning the Hamiltonian for varying spatial measurement resolutions gives access to field theories at different energy scales, and allows to learn a flow of Hamiltonians reminiscent of the renormalization group. Our method, which we demonstrate in both theoretical studies and available data from a quantum gas experiment, promises new ways of addressing the emergence of quantum field theories in quantum simulation experiments.
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A. Warman, F. Yang, A. Tiwari, H. Pichler, S. Schafer-Nameki Categorical Symmetries in Spin Models with Atom Arrays,
Phys. Rev. Lett. 135 206503 (2024-11-13),
http://dx.doi.org/10.1103/249m-m8wq doi:10.1103/249m-m8wq
Categorical symmetries have recently been shown to generalize the classification of phases of matter, significantly broadening the traditional Landau paradigm. To test these predictions, we propose a simple spin chain model that encompasses all gapped phases and second-order phase transitions governed by the categorical symmetry Rep(D8). This model not only captures the essential features of non-invertible phases but is also straightforward enough to enable practical realization. Specifically, we outline an implementation using neutral atoms trapped in optical tweezer arrays. Employing a dual-species setup and Rydberg blockade, we propose a digital simulation approach that can efficiently implement the many-body evolution in several nontrivial quantum phases.
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G. Giudici, F. M. Surace, H. Pichler Unraveling PXP Many-Body Scars through Floquet Dynamics,
Phys. Rev. Lett. 133 190404 (2024-11-08),
http://dx.doi.org/10.1103/PhysRevLett.133.190404 doi:10.1103/PhysRevLett.133.190404
Quantum scars are special eigenstates of many-body systems that evade thermalization. They were first discovered in the PXP model, a well-known effective description of Rydberg atom arrays. Despite significant theoretical efforts, the fundamental origin of PXP scars remains elusive. By investigating the discretized dynamics of the PXP model as a function of the Trotter step τ, we uncover a remarkable correspondence between the zero- and two-particle eigenstates of the integrable Floquet-PXP cellular automaton at τ=π/2 and the PXP many-body scars of the time-continuous limit. Specifically, we demonstrate that PXP scars are adiabatically connected to the eigenstates of the τ=π/2 Floquet operator. Building on this result, we propose a protocol for achieving high-fidelity preparation of PXP scars in Rydberg atom experiments.
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C. Fromonteil, R. Tricarico, F. Cesa, H. Pichler Hamilton-Jacobi-Bellman equations for Rydberg-blockade processes,
Phys. Rev. Research 6 33333 (2024-09-24),
http://dx.doi.org/10.1103/PhysRevResearch.6.033333 doi:10.1103/PhysRevResearch.6.033333
We discuss time-optimal control problems for two setups involving globally driven Rydberg atoms in the blockade limit by deriving the associated Hamilton-Jacobi-Bellman equations. From these equations, we extract the globally optimal trajectories and the corresponding controls for several target processes of the atomic system, using a generalized method of characteristics. We apply this method to retrieve known results for CZ and C-phase gates, and to find new optimal pulses for all elementary processes involved in the universal quantum computation scheme introduced in [Physical Review Letters 131, 170601 (2023)].
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K. Vodenkova, H. Pichler Continuous Coherent Quantum Feedback with Time Delays: Tensor Network Solution,
Phys. Rev. X 14 31043 (2024-09-09),
http://dx.doi.org/10.1103/PhysRevX.14.031043 doi:10.1103/PhysRevX.14.031043
In this paper we develop a novel method to solve problems involving quantum optical systems coupled to coherent quantum feedback loops featuring time delays. Our method is based on exact mappings of such non-Markovian problems to equivalent Markovian driven dissipative quantum many-body problems. In this work we show that the resulting Markovian quantum many-body problems can be solved (numerically) exactly and efficiently using tensor network methods for a series of paradigmatic examples, consisting of driven quantum systems coupled to waveguides at several distant points. In particular, we show that our method allows solving problems in so far inaccessible regimes, including problems with arbitrary long time delays and arbitrary numbers of excitations in the delay lines. We obtain solutions for the full real-time dynamics as well as the steady state in all these regimes. Finally, motivated by our results, we develop a novel mean-field approach, which allows us to find the solution semi-analytically and identify parameter regimes where this approximation is in excellent agreement with our exact tensor network results.
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T. Vovk, H. Pichler Quantum trajectory entanglement in various unravelings of Markovian dynamics,
Phys. Rev. A 110 12207 (2024-07-08),
http://dx.doi.org/10.1103/PhysRevA.110.012207 doi:10.1103/PhysRevA.110.012207
The cost of classical simulations of quantum many-body dynamics is often determined by the amount of entanglement in the system. In this paper, we study entanglement in stochastic quantum trajectory approaches that solve master equations describing open quantum system dynamics. First, we introduce and compare adaptive trajectory unravelings of master equations. Specifically, building on [Phys. Rev. Lett. 128, 243601 (2022)], we study several greedy algorithms that generate trajectories with a low average entanglement entropy. Second, we consider various conventional unravelings of a one-dimensional open random Brownian circuit and locate the transition points from area- to volume-law-entangled trajectories. Third, we compare various trajectory unravelings using matrix product states with a direct integration of the master equation using matrix product operators. We provide concrete examples of dynamics, for which the simulation cost of stochastic trajectories is exponentially smaller than the one of matrix product operators.
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Z. J. Li, G. Giudici, H. Pichler Variational manifolds for ground states and scarred dynamics of blockade-constrained spin models on two and three dimensional lattices,
Phys. Rev. Research 6 23146 (2024-05-09),
http://dx.doi.org/10.1103/PhysRevResearch.6.023146 doi:10.1103/PhysRevResearch.6.023146
We introduce a variational manifold of simple tensor network states for the study of a family of constrained models that describe spin-1/2 systems as realized by Rydberg atom arrays. Our manifold permits analytical calculation via perturbative expansion of one- and two-point functions in arbitrary spatial dimensions and allows for efficient computation of the matrix elements required for variational energy minimization and variational time evolution in up to three dimensions. We apply this framework to the PXP model on the hypercubic lattice in 1D, 2D, and 3D, and show that, in each case, it exhibits quantum phase transitions breaking the sub-lattice symmetry in equilibrium, and hosts quantum many body scars out of equilibrium. We demonstrate that our variational ansatz qualitatively captures all these phenomena and predicts key quantities with an accuracy that increases with the dimensionality of the lattice, and conclude that our method can be interpreted as a generalization of mean-field theory to constrained spin models.
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V. S. Ferreira, G. Kim, A. Butler, H. Pichler, O. Painter Deterministic Generation of Multidimensional Photonic Cluster States with a Single Quantum Emitter,
Nature Phys. 20 870 (2024-02-28),
http://dx.doi.org/10.1038/s41567-024-02408-0 doi:10.1038/s41567-024-02408-0
Multidimensional photonic graph states, such as cluster states, have prospective applications in quantum metrology, secure quantum communication, and measurement-based quantum computation. However, to date, generation of multidimensional cluster states of photonic qubits has relied on probabilistic methods that limit the scalability of typical generation schemes in optical systems. Here we present an experimental implementation in the microwave domain of a resource-efficient scheme for the deterministic generation of 2D photonic cluster states. By utilizing a coupled resonator array as a slow-light waveguide, a single flux-tunable transmon qubit as a quantum emitter, and a second auxiliary transmon as a switchable mirror, we achieve rapid, shaped emission of entangled photon wavepackets, and selective time-delayed feedback of photon wavepackets to the emitter qubit. We leverage these capabilities to generate a 2D cluster state of four photons with 70\% fidelity, as verified by tomographic reconstruction of the quantum state. We discuss how our scheme could be straightforwardly extended to the generation of even larger cluster states, of even higher dimension, thereby expanding the scope and practical utility of such states for quantum information processing tasks.
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I. Cong, N. Maskara, M. C. Tran, H. Pichler, G. Semeghini, S. F. Yelin, S. Choi, M. Lukin Enhancing Detection of Topological Order by Local Error Correctio,
Nat. Commun. 15 1527 (2024-02-20),
http://dx.doi.org/10.1038/s41467-024-45584-6 doi:10.1038/s41467-024-45584-6
The exploration of topologically-ordered states of matter is a long-standing goal at the interface of several subfields of the physical sciences. Such states feature intriguing physical properties such as long-range entanglement, emergent gauge fields and non-local correlations, and can aid in realization of scalable fault-tolerant quantum computation. However, these same features also make creation, detection, and characterization of topologically-ordered states particularly challenging. Motivated by recent experimental demonstrations, we introduce a new approach for quantifying topological states -- locally error-corrected decoration (LED) -- by combining methods of error correction with ideas of renormalization-group flow. Our approach allows for efficient and robust identification of topological order, and is applicable in the presence of incoherent noise sources, making it particularly suitable for realistic experiments. We demonstrate the power of LED using numerical simulations of the toric code under a variety of perturbations, and we subsequently apply it to an experimental realization of a quantum spin liquid using a Rydberg-atom quantum simulator. Extensions to the characterization of other exotic states of matter are discussed.