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M. John, K. Pareek, P. Tirler, T. Gollerthan, M. Meth, L. Gerster, P. Zoller, D. González-Cuadra, T. Zache, M. Ringbauer Non-Abelian String-Breaking Dynamics on a Qudit Quantum Computer,
(2026-05-07),
arXiv:2605.05841 arXiv:2605.05841
Gauge theories form the foundation of the Standard Model of particle physics. These theories can exhibit confinement, where charged particles only occur in bound states, connected by flux strings whose energy grows linearly with separation. Simulating the real-time dynamics of such strings, including their breaking, remains a major challenge for classical computations and a promising target for quantum simulations. While recent quantum simulation experiments explored string-breaking dynamics in abelian lattice gauge theories, non-abelian theories are qualitatively distinct because gauge fields themselves carry charge. Here, we report the first quantum simulation of genuine non-abelian string-breaking dynamics in a pure SU(2) lattice gauge theory, where gauge-field self-interactions drive string breaking even in the absence of dynamical matter. Our results are obtained on a trapped-ion quantum computer, using native qudit Hilbert spaces to encode truncated gauge fields on a ladder geometry and implement digital Trotter dynamics. We experimentally study unbreakable and breakable strings generated by fundamental and adjoint static charges, respectively. We locally resolve string oscillations and coherent string breaking through the creation of gluonic excitations driven by non-abelian plaquette interactions. Our work establishes hardware-efficient, problem-tailored qudit simulations as a promising route for accessing non-perturbative dynamics relevant to high-energy physics.
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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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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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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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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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H. Froland, T. Zache, R. Ott, N. Müller Entanglement Structure of Non-Gaussian States and How to Measure It,
Phys. Rev. Lett. 135 40201 (2025-07-23),
http://dx.doi.org/10.1103/pnp2-g1g5 doi:10.1103/pnp2-g1g5
Rapidly growing capabilities of quantum simulators to probe quantum many-body phenomena require new methods to characterize increasingly complex states. We present a protocol that constrains quantum states using experimentally measured correlation functions. This method enables measurement of a quantum state’s entanglement structure, opening a new route to study entanglement-related phenomena. Our approach extends Gaussian state parameterizations by systematically incorporating higher-order correlations. We show the protocol’s usefulness in conjunction with current and forthcoming experimental capabilities, focusing on weakly interacting fermions as a proof of concept. Here, the lowest nontrivial expansion quantitatively predicts early time thermalization dynamics, including signaling the onset of quantum chaos indicated by the entanglement Hamiltonian.
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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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A. Kruckenhauser, M. Yuan, H. Zheng, M. Mamaev, P. Zeng, X. M. Mao, Q. Xu, T. Zache, L. Jiang, R. van Bijnen, P. Zoller Dark spin-cats as biased qubits,
Phys. Rev. Lett. 135 20601 (2025-07-08),
http://dx.doi.org/10.1103/w9zh-jwsx doi:10.1103/w9zh-jwsx
We present a biased atomic qubit, universally implementable across all atomic platforms, encoded as a `spin-cat' within ground state Zeeman levels. The key characteristic of our configuration is the coupling of the ground state spin manifold of size Fg≫1 to an excited Zeeman spin manifold of size Fe=Fg−1 using light. This coupling results in eigenstates of the driven atom that include exactly two dark states in the ground state manifold, which are decoupled from light and immune to spontaneous emission from the excited states. These dark states constitute the `spin-cat', leading to the designation `dark spin-cat'. We demonstrate that under strong Rabi drive and for large Fg, the `dark spin-cat' is autonomously stabilized against common noise sources and encodes a qubit with significantly biased noise. Specifically, the bit-flip error rate decreases exponentially with Fg relative to the dephasing rate. We provide an analysis of dark spin-cats, their robustness to noise, and discuss bias-preserving single qubit and entangling gates, exemplified on a Rydberg tweezer platform.
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D. Gonzalez Cuadra, M. Hamdan, T. Zache, B. Braverman, M. Kornjaca, A. Lukin, S. H. Cantu, F. Liu, S. Wang, A. Keesling, M. Lukin, P. Zoller, A. Bylinskii Observation of string breaking on a (2 + 1)D Rydberg quantum simulator,
Nature 462 326 (2025-06-04),
http://dx.doi.org/10.1038/s41586-025-09051-6 doi:10.1038/s41586-025-09051-6
Lattice gauge theories (LGTs) describe a broad range of phenomena in condensed matter and particle physics. A prominent example is confinement, responsible for bounding quarks inside hadrons such as protons or neutrons. When quark-antiquark pairs are separated, the energy stored in the string of gluon fields connecting them grows linearly with their distance, until there is enough energy to create new pairs from the vacuum and break the string. While such phenomena are ubiquitous in LGTs, simulating the resulting dynamics is a challenging task. Here, we report the observation of string breaking in synthetic quantum matter using a programmable quantum simulator based on neutral atom arrays. We show that a (2+1)D LGT with dynamical matter can be efficiently implemented when the atoms are placed on a Kagome geometry, with a local U(1) symmetry emerging from the Rydberg blockade, while long-range Rydberg interactions naturally give rise to a linear confining potential for a pair of charges, allowing us to tune both their masses as well as the string tension. We experimentally map out the corresponding phase diagram by adiabatically preparing the ground state of the atom array in the presence of defects, and observe substructure of the confined phase, distinguishing regions dominated by fluctuating strings or by broken string configurations. Finally, by harnessing local control over the atomic detuning, we quench string states and observe string breaking dynamics exhibiting a many-body resonance phenomenon. Our work paves a way to explore phenomena in high-energy physics using programmable quantum simulators.
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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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J. Berges, S. Brandstetter, J. Brewer, G. Bruun, T. Enss, S. Floerchinger, K. Fujii, M. Galka, G. Giacalone, Q. Guan, C. Heintze, L. Heyen, I. Selyuzhenkov, S. Jochim, J. Levinsen, P. Lunt, S. Masiocchi, A. Mazeliauskas, N. Navon, A. Ohlson, M. Parish, S. Few is different: deciphering many-body dynamics in mesoscopic quantum gases,
(2025-09-05),
arXiv:2509.05049 arXiv:2509.05049
Emergent macroscopic descriptions of matter, such as hydrodynamics, are central to our description of complex physical systems across a wide spectrum of energy scales. The conventional understanding of these many-body phenomena has recently been shaken by a number of experimental findings. Collective behavior of matter has been observed in \emph{mesoscopic} systems, such as high-energy hadron-hadron collisions, or ultra-cold gases with only few strongly interacting fermions. In such systems, the separation of scales between macroscopic and microscopic dynamics (at the heart of any effective theory) is inapplicable. To address the conceptual challenges that arise from these observations and explore the universality of emergent descriptions of matter, the EMMI Rapid Reaction Task Force was assembled. This document summarizes the RRTF discussions on recent theoretical and experimental advances in this rapidly developing field. Leveraging technological breakthroughs in the control of quantum systems, we can now quantitatively explore what it means for a system to exhibit behavior beyond the sum of its individual parts. In particular, the report highlights how the (in)applicability of hydrodynamics and other effective theories can be probed across three principal frontiers: the size frontier, the equilibrium frontier, and the interaction frontier.
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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.