Simulation of far-from-equilibrium quantum many-body dynamics (SimQuDyn)

14.04.2025, 08:00 → 17.04.2025, 20:00 Europe/Berlin

B052 (ASC)

Simulation of far-from-equilibrium quantum many-body dynamics (SimQuDyn) is a conference bringing together researchers and students in the fields of classical and quantum simulation of far-from-equilibrium quantum many-body dynamics, as well as analytical approaches to the latter. The goal of this conference is the discussion and exchange of ideas related to the latest advances in these fields and to chart a path forward that includes collaborative efforts between them. A main point of discussion will be using far-from-equilibrium quantum many-body dynamics as a venue to achieve practical quantum advantage.

 

Confirmed Speakers:

• Yevgeny Bar Lev (Ben Gurion University of the Negev)
• Alejandro Bermúdez (IFT-CSIC)
• Hannes Bernien (University of Chicago)
• Berislav Buča (University of Copenhagen)
• Marin Bukov (MPIPKS)
• Anushya Chandran (Boston University)
• Soonwon Choi (MIT)
• Zohreh Davoudi (University of Maryland)
• Jean-Yves Desaules (ISTA)
• Giuseppe De Tomasi (University of Lisbon)
• Thomas Iadecola (Iowa State University)
• Thierry Lahaye (Institut d'Optique)
• Achilleas Lazarides (Loughborough University)
• Julian Léonard (TU Wien)
• Sophie Li (Harvard University)
• Andrew Lucas (University of Colorado, Boulder)
• Lesik Motrunich (Caltech)
• Sanjay Moudgalya (TUM)
• Sara Murciano (Caltech)
• Zlatko Papić (University of Leeds)
• Frank Pollmann (TUM)
• Tibor Rakovszky (BME)
• Enrico Rinaldi (Quantinuum)
• Martin Ringbauer (University of Innsbruck)
• Pedram Roushan (Google Quantum AI)
• Rhine Samajdar (Princeton University)
• Uli Schollwöck (LMU Munich)
• Mark Stone (Atom Computing)
• Roman Vasseur (University of Massachusetts Amherst)
• Vladan Vuletic (MIT)
• Pascal Weckesser (MPQ)
• Zhen-Sheng Yuan (USTC)

Organizers:

Monika Aidelsburger (MPQ, LMU), Jad C. Halimeh (MPQ, LMU), and Pablo Sala (Caltech)

 

Mo., 14. April ¶

08:30 Name-tag and MCQST merch pickup

09:10 SimQuDyn opening statement by Jad Halimeh

1 Complex time and real materials¶

The simulation of correlated real materials remains one of the big challenges of solid state physics, in particular due to the fact that the physical behaviour is often determined by energy scales which are extremely small compared to the raw scales of the substances. In this talk I will discuss how extending time evolution into the complex plane alleviates entanglement issues to an extent that we may calculate precise Green’s functions, self-energies and spectral functions at very low frequencies (of the order of 0.001 of bandwidth), which is the scale that has to be resolved to understand correlated metals in a realistic setting.

Sprecher: Prof. Uli Schollwöck (LMU Munich)

2 TBA¶

TBA

Sprecher: Prof. Zlatko Papić (University of Leeds)

10:30 Coffee break

3 Towards Quantum Simulation with Qudits¶

Information-theoretic quantities, such as Rényi entropies, exhibit remarkable universality in their late-time behavior across a wide range of chaotic quantum many-body systems. Understanding how these common features arise from vastly different microscopic dynamics remains an important challenge. In this talk, I will show this mechanism for a class of one-dimensional Brownian models with random, time-dependent Hamiltonians and a variety of microscopic couplings. In these models, the real-time Lorentzian evolution of the n-th Rényi entropy can be mapped onto an imaginary time Euclidean evolution of an effective Hamiltonian acting on 2n copies of the system. In the absence of symmetries, the ground states of this effective Hamiltonian resemble ferromagnets, hence its low-energy excitations are gapped domain walls between these ferromagnetic ground states. I will demonstrate how the membrane picture of entanglement growth naturally emerges from the physics of these domain-wall excitations, and show that the membrane tension is determined by their dispersion relation. While this prescription works straightforwardly for the computation of the membrane tension for the second Rényi entropy, there are subtleties that arise for higher Rényi entropies, which I will discuss. In all, this framework provides a universal understanding of entanglement dynamics in one dimension in terms of gapped low-lying modes, with potential extensions to non-random systems governed by time-independent Hamiltonians. Finally, I will discuss the fate of this picture in the presence of measurements, symmetries, and in higher-dimensional settings.

Sprecher: Prof. Martin Ringbauer (University of Innsbruck)

4 Quantum gas microscopy of Rydberg-dressed quantum systems¶

The competition of different length and energy scales in quantum many-body systems leads to various novel phenomena, including the emergence of correlated dynamics or non-local order. "Rydberg dressing", off-resonant optical coupling of an atomic ground state to a Rydberg state, enables to engineer long-range interactions on a micrometer scale, making it a powerful tool for studying correlated dynamics in lattice-based atomic quantum simulators. In our experiment, we leverage this tunability to realize a one-dimensional extended Bose Hubbard model for 87Rb atoms trapped in optical lattices. Unlike before, we enter the itinerant regime by applying stroboscopic dressing, reducing collective losses by two orders of magnitude. Operating at either low or high filling, we study the correlated out-of-equilibrium dynamics of extended-range repulsively-bound pair states or the near equilibrium density ordering when applying adiabatic ramps. Our findings pave the way to study itinerant, coupled ladder systems, and spin-breaking in stationary spin chains.

Sprecher: Dr. Pascal Wecksser (MPQ)

12:00 Lunch

5 Probing Non-Equilibrium Topological Order on a Quantum Processor¶

Out-of-equilibrium phases in many-body systems constitute a new paradigm in quantum matter - they exhibit dynamical properties that may otherwise be forbidden by equilibrium thermodynamics. Among these non-equilibrium phases are periodically driven (Floquet) systems, that are generically difficult to simulate classically due to their high entanglement. Using an array of superconducting qubits, we realize a Floquet topologically ordered state, image the characteristic dynamics of its chiral edge modes, and characterize its emergent anyonic excitations. Devising an interferometric algorithm allows us to introduce and measure a bulk topological invariant to probe the dynamical transmutation of anyons for system sizes up to 58 qubits. Our work demonstrates that quantum processors can provide key insights into the thus-far largely unexplored landscape of highly entangled non-equilibrium phases of matter.

Sprecher: Prof. Frank Pollmann (TUM)

6 Ergodicity Breaking, Localization and Kinetic Constraints (in East-type models)¶

I will report on work, both published and unpublished, on constrained East type models.

Sprecher: Prof. Achilleas Lazarides (Loughborough University)

14:30 Coffee break

7 Anomalous diffusive fluctuations in low-dimensional quantum systems¶

Starting from a pure initial state, the local properties of chaotic many-body quantum systems are expected to quickly thermalize under unitary dynamics. The remaining evolution from local to global equilibrium is described by the classical equations of hydrodynamics. However, the advent of quantum simulator platforms has made it possible to measure not only local expectation values, but also their full quantum statistics, fluctuations and space-time correlations. In this talk, I will discuss a theory of diffusive fluctuations in chaotic many-body quantum systems, and establish its validity in random unitary quantum circuits with charge conservation. I will also discuss exceptions to this conventional behavior in integrable quantum spin chains, as well as Dirac fluids as a result of Lorentz invariance and particle-hole symmetry. In particular, I will argue that charge noise in the hydrodynamic regime of Dirac fluids and of some two-component classical gases is parametrically enhanced relative to that in conventional diffusive metals.

Sprecher: Prof. Romain Vasseur (University of Geneva)

8 Bottlenecks of quantum channels and their application to quantum spin glass order in LDPC codes¶

We prove an analogue of the “bottleneck theorem”, well-known for classical Markov chains, for Markovian quantum channels. In particular, we show that if two regions (subspaces) of Hilbert space are separated by a region that has very low weight in the channel’s steady state, then states initialized on one side of this barrier will be stuck for a long time. This puts a lower bound on the mixing time in terms of an appropriately defined “quantum bottleneck ratio”, which involves both diagonal and off-diagonal matrix elements of the steady state density matrix. Specializing to the case of finite temperature Gibbs states of a quantum many-body systems, the bottleneck theorem provides a novel, dynamical perspective on non-trivial phases of matter in terms of a decomposition of the Gibbs state into multiple components separated by bottlenecks. We use this perspective to motivate the definition of "topological quantum spin glass" (TQSG) order, which combines features of certain classical spin glass models with those of topologically ordered systems. We prove that TQSG order is realized at low temperatures in a large class of quantum low-density parity check (qLDPC) codes defined on expander graphs.

Sprecher: Prof. Tibor Rakovszky (Budapest University of Technology and Economics)

Di., 15. April ¶

9 Neutral-atom arrays for cavity QED¶

Arrays of individually trapped neutral atoms are arising as a new tool for applications ranging from quantum computing to precision spectroscopy. Using Rydberg interactions, high-fidelity quantum gates can be realized in such systems. I will report on experiments where arrays of atoms are coupled to high-finesse optical cavities, enabling fast state detection, adaptive measurements and control, and the real-time observation of individual atomic-collisions events. I will also discuss prospects and opportunities for integrating cavity QED and Rydberg systems.

Sprecher: Prof. Vladan Vuletić (MIT)

10 Novel quantum dynamics with superconducting qubits¶

In recent years, superconducting qubits have emerged as a leading platform for quantum simulation, particularly for studying quantum dynamics on Noisy Intermediate-Scale Quantum (NISQ) processors. I will discuss some of our work within this broad area of research. In a recent study [1], we directly image the dynamics of charges and strings in (2+1)-dimensional lattice gauge theories. We identify two distinct regimes within the confining phase: in the weak confinement regime, the string exhibits strong transverse fluctuations, while in the strong confinement regime, these fluctuations are significantly suppressed. In another study [2], we observe a novel form of localization in quantum many-body systems in one and two dimensions. Despite the absence of disorder, energy perturbations do not spread, even when both the evolution operator and initial states are fully translationally invariant. These results demonstrate that NISQ processors—in the absence of fully developed quantum computers—are invaluable tools for probing non-equilibrium physics, offering critical insights into complex quantum dynamics.
[1] Cochran et al., arxiv.org/abs/2409.17142
[2] Gyawali et al., arxiv.org/abs/2410.06557

Sprecher: Dr. Pedram Roushan (Google Quantum AI)

10:30 Coffee break

11 TBA¶

TBA

Sprecher: Prof. Soonwon Choi (MIT)

12 Geometric Floquet theory¶

We derive Floquet theory from quantum geometry. We identify quasienergy folding as a consequence of a broken gauge group of the adiabatic gauge potential U(1)↦Z. Fixing instead the gauge freedom using the parallel-transport gauge uniquely decomposes Floquet dynamics into a purely geometric and a purely dynamical evolution. The dynamical average-energy operator provides an unambiguous sorting of the quasienergy spectrum, identifying a unique Floquet ground state and suggesting a way to define the filling of Floquet-Bloch bands. We exemplify the features of geometric Floquet theory using an exactly solvable XY model and a non-integrable kicked Ising chain. We elucidate the geometric origin of inherently nonequilibrium effects, like the π-quasienergy gap in discrete time crystals or π-edge modes in anomalous Floquet topological insulators. The spectrum of the average-energy operator is a susceptible indicator for both heating and spatiotemporal symmetry-breaking transitions. Last, we demonstrate that the periodic lab frame Hamiltonian generates transitionless counterdiabatic driving for Floquet eigenstates. This work directly bridges seemingly unrelated areas of nonequilibrium physics.

Sprecher: Dr. Marin Bukov (MPIPKS)

12:00 Lunch

13 Nonequilibrium processes in gauge theories: quantum-thermodynamics, quantum-information, and quantum-simulation perspectives¶

Quantum simulation is a promising route to studying nonequilibrium physics of strongly-coupled quantum systems, including gauge theories of relevance to nuclear and high-energy physics. We develop a quantum-thermodynamic framework to study lattice gauge theories in and out of equilibrium, focusing on protocols which can be implemented in quantum simulations, and finding thermodynamic quantities that can signal phase transitions reliably. We then suggest a tool in quantum information science, namely entanglement-Hamiltonian tomography, to measure these quantities. We further discuss how the entanglement Hamiltonian of gauge theories can be measured, and how early signals of thermalization can be deduced from its spectrum, via a demonstration in a (2+1)D gauge theory using a digital quantum computer. Finally, toward the ultimate goal of simulating high-energy collisions and the early universe, we briefly overview our effort in simulating string-breaking dynamics in quanch, adiabatic, and controlled diabatic processes in quantum-spin chains using a trapped-ion analog quantum simulator.

Sprecher: Prof. Zohreh Davoudi (University of Maryland)

14 The Creutz-Hubbard toolbox: mimicking particle production and chiral waves in Gross-Neveu models¶

In this talk, I will discuss how ultra cold atoms in Raman optical lattices can serve as quantum simulators of Gross-Neveu QFTs. I will describe our recent studies related to particle production and entanglement dynamics in analogue expanding spacetimes, and how finite-density crystalline phases related to inhomogeneous chiral condensates could be accessed by varying the atomic filling.

Sprecher: Prof. Alejandro Bermúdez (IFT-CSIC)

14:30 Coffee break

15 Ordered phases of matter at arbitrarily high temperature¶

Ordinarily we think that at high enough temperatures, systems become disordered and are in a thermodynamically trivial phase. For classical and quantum lattice models of interacting spins, theorems indeed prove that there is no long-range order or entanglement above a sufficiently high temperature. I will show how it is nevertheless possible to engineer models that order at arbitrarily high temperature, using interacting bosons. Explicit and simple constructions for solids, magnets, superfluids and even quantum topological order, at arbitrarily high temperature, will be presented. All such models exhibit “entropic order”: ordering one degree of freedom (e.g. spins) can enable a boson to more strongly fluctuate; the entropy of these fluctuations can dominate the thermal ensemble at high temperature. Infinities in bosonic models can therefore qualitatively change statistical physics.

Sprecher: Prof. Andrew Lucas (University of Colorado Boulder)

16 Probing symmetries in out-of-equilibrium quantum systems¶

In the study of out-of-equilibrium many-body quantum systems, growing attention has been given to understanding how symmetries evolve over time under unitary dynamics. Key questions include whether symmetries are dynamically restored in local subsystems and how the timescales involved depend on the initial states and the dynamics of the system. In this talk, we introduce the entanglement asymmetry as a versatile and practical tool for probing symmetry breaking and restoration in extended quantum systems. Specifically, we investigate the evolution of a symmetry that is initially preserved but subsequently broken by random unitary dynamics. At late times, the system's behavior matches that of a random state of qubits. Finally, we will show that, in setups where the symmetry is restored, the entanglement asymmetry neatly detects an unexpected quantum version of the Mpemba effect.

Sprecher: Dr. Sara Murciano (Université Paris-Saclay - LPTMS)

16:00 Group photo

16:15 Poster session

Mi., 16. April ¶

17 Concomitant Entanglement and Control Criticality Driven by Collective Measurements¶

Adaptive quantum circuits—where a quantum many-body state is controlled using measurements and conditional unitary operations—are a powerful paradigm for state preparation and quantum error-correction tasks. They can support two types of nonequilibrium quantum phase transitions: measurement-induced transitions between volume- and area-law-entangled steady states and control-induced transitions where the system falls into an absorbing state or, more generally, an orbit visiting several absorbing states. Within this context, nonlocal conditional operations can alter the critical properties of the two transitions and the topology of the phase diagram. Here, we consider the scenario where the measurements are nonlocal, in order to engineer efficient control onto dynamical trajectories. Motivated by Rydberg-atom arrays, we consider a locally constrained model with global sublattice magnetization measurements and local correction operations to steer the system’s dynamics onto a many-body orbit with finite recurrence time. The model has a well-defined classical limit, which we leverage to aid our analysis of the control transition. As a function of the density of local correction operations, we find control and entanglement transitions with continuously varying critical exponents. For sufficiently high densities of local correction operations, we find that both transitions acquire a dynamical critical exponent 𝑧 <1, reminiscent of criticality in long-range power-law interacting systems. At low correction densities, we find that the criticality reverts to a short-range nature with 𝑧 ≳1. In the long-range regime, the control and entanglement transitions are indistinguishable to within the resolution of our finite-size numerics, while in the short-range regime we find evidence that the transitions become distinct. We conjecture that the effective long-range criticality mediated by collective measurements is essential in driving the two transitions together.

Sprecher: Prof. Thomas Iadecola (Iowa State University)

18 Discovering with trapped-ion gate-based quantum computers: from magnetism to quantum gravity¶

We highlight two key experimental breakthroughs achieved using the QCCD trapped-ion Quantinuum Systems. First, by simulating digitized dynamics of the quantum Ising model, we observed Floquet prethermalization and local equilibration at circuit volumes exceeding 2000 gates, beyond classical simulation capabilities. Second, leveraging a randomized quantum algorithm, we successfully simulated the real-time dynamics of a sparsified Sachdev-Ye-Kitaev (SYK) model—known for exhibiting quantum chaotic behavior—on the same hardware. Enhanced by high-fidelity quantum operations and full qubit connectivity, we captured the decay of return probabilities in this fermionic system, demonstrating the potential of quantum processors for investigating quantum gravitational models. Together, these results showcase the powerful capabilities of trapped-ion gate-based quantum computers in addressing frontier questions in strongly correlated quantum many body systems.

Sprecher: Dr. Enrico Rinaldi (Quantinuum)

10:30 Coffee break

19 Eternal equilibrium¶

I will provide a framework for computing time-averaged dynamics in locally interacting systems in any dimension. It is based on pseudolocal dynamical symmetries generalising pseudolocal charges and unifies seemingly disparate manifestations of quantum non-ergodic dynamics including quantum many-body scars, continuous, discrete and dissipative time crystals, Hilbert space fragmentation, lattice gauge theories, and disorder-free localization. Using the theory two novel types of phase transitions are introduced: 1) The "scarring phase transition" where the order parameter is the locality of the projected local quantities - for certain initial states persistent oscillations are present. 2) The "fragmentation phase transition" for which long-range order is established in an entire phase due to presence of certain non-local strings. Two prototypical, but otherwise mostly intractable, models are solved exactly using the theory: 1) a spin 1 scarred model and 2) the t-J_z model with fragmentation. I will further discuss a novel method for using Krylov subspace methods to construct the dynamical symmetries - in particular, by introducing an environment to the Krylov chain.

References:
N. Loizeau, B. Buca, D. Sels.arXiv:2503.07403 (2025).
B. Buca. Phys. Rev. X 13, 031013 (2023).
D. E. Parker, X. Cao, A. Avdoshkin, T. Scaffidi, E. Altman. Phys. Rev. X 9, 041017 (2019).
B. Doyon. Commun. Math. Phys. 351, 155 (2017).

Sprecher: Prof. Berislav Buča (Université Paris-Saclay)

20 New exact scars in the PXP and related models¶

The original PXP chain that opened experimentally the field of quantum many-body scars continues to surprise us. I will first describe discovery [1] of exact volume-entangled eigenstates in this and many related models (including in higher dimensions). I will then describe finding [2] of several new exact scars with finite bond dimension in the PXP chain, including some that provide an excellent description of so-called Z2 scars observed in exact diagonalization and the associated long-lived revivals in quenches from the Z2 CDW state. I will speculate on the possibility that the PXP chain harbors yet more exact scars of increasing complexity that may be progressively more difficult to find.

[1] "Volume-entangled exact eigenstates in the PXP and related models in any dimension," A. N. Ivanov and O. I. Motrunich, Phys. Rev. Lett. 134, 050403 (2025).
[2] "Many exact area-law scar eigenstates in the nonintegrable PXP and related models," A. N. Ivanov and O. I. Motrunich, arXiv:2503.16327

Sprecher: Prof. Olexei Motrunich (Caltech)

12:00 Lunch

21 Quantum coarsening and collective dynamics on a programmable quantum simulator¶

Dynamics driven by quantum fluctuations are important for the formation of exotic quantum phases of matter, fundamental high-energy processes, quantum metrology, and quantum algorithms. In this talk, I will the describe our use of a programmable quantum simulator based on Rydberg atom arrays to experimentally study collective dynamics across a (2+1)D Ising quantum phase transition. After crossing the quantum critical point, we observe a gradual growth of correlations through coarsening of antiferromagnetically ordered domains. Furthermore, by deterministically preparing and following the evolution of ordered domains, we show that the coarsening is driven by the curvature of domain boundaries and find that the dynamics accelerate with proximity to the quantum critical point. We quantitatively explore these phenomena and further observe long-lived oscillations of the order parameter, corresponding to an amplitude (Higgs) mode. These observations offer a unique viewpoint into emergent collective dynamics in strongly correlated quantum systems and non-equilibrium quantum processes.

Sprecher: Dr. Sophie Li (Harvard University)

22 Quantum dynamics on a dual-species Rydberg array¶

Reconfigurable arrays of neutral atoms have emerged as a leading platform for quantum science. Their excellent coherence properties combined with programmable Rydberg interactions have led to intriguing observations such as quantum phase transitions, the discovery of quantum many-body scars, and novel quantum computing architectures.
Here, I am introducing a dual-species Rydberg array that naturally lends itself for measurement-based protocols such as quantum error correction, long-range entangled state preparation, and measurement-altered many-body dynamics. Furthermore, Rydberg interactions between the two species then lead to novel regimes, including greatly enhanced resonant dipole interactions, that we use to demonstrate a two-qubit gate and quantum non-demolition readout [2].
I will present our current experiments on implementing a quantum cellular automata in a dual-species array. Cellular automata are famous for producing complex behavior as well as universal computation based on simple initial states and update rules. Here we investigate this paradigm by implementing an update rule based on dual species Rydberg blockade and periodic driving. We investigate connections to thermalization [2] and quantum information processing [3].

[1] Anand, Bradley, White, Ramesh, Singh, Bernien, Nature Physics 20, 1744 (2024). [2] Iadecola and Vijay. Phys. Rev. B 102(18), 180302 (2020). [3] Cesa and Pichler, PRL 131, 170601.

Sprecher: Prof. Hannes Bernien (University of Innsbruck)

14:30 Coffee break

23 Ergodicity and Entanglement: Bridging Random Matrix Theory and Many-Body Quantum Systems¶

Thermalization is deeply connected to the notion of ergodicity in Hilbert space, implying the equipartition of the wave function over the available many-body Fock states. Under unitary time evolution, an initially structured state spreads in Fock space, approaching a Haar-random state, thereby revealing a deep connection between many-body quantum systems and random matrix theory.
In the first part of this talk, I will discuss the dynamics of the self-dual kicked Ising model, a minimal model of many-body quantum chaos that is unitary in both time and space. I will focus on its evolution in Fock space, showing how the probability distribution of the initial state approaches that of a random state, characterized by the Porter-Thomas distribution.
In the second part, I will explore general relationships between entanglement and the spread of the wave function in Fock space. I will demonstrate that entanglement entropies can still exhibit fully ergodic behavior, even when the wave function occupies only a vanishing fraction of the full Hilbert space in the thermodynamic limit.

Sprecher: Prof. Giuseppe De Tomasi (Universidade de Lisboa)

24 Beyond the Born-Oppenheimer Approximation: entanglement, squeezing and synchronization¶

I will describe a mixed quantum-classical framework, dubbed the Moving Born-Oppenheimer Approximation (MBOA), to describe the dynamics of slow degrees of freedom coupled to fast ones. The key assumption is that the fast degrees of freedom adiabatically follow a state that depends on the position and momenta of the slow degrees of freedom. The MBOA reveals rich dynamics; for example, the fast degrees of freedom can get entangled and squeezed, and their motion can synchronize with that of the slow degrees of freedom. I will describe these effects in model classical and quantum systems, and discuss potential applications in molecular dynamics, state preparation, and quantum sensing.

Sprecher: Prof. Anushya Chandran (Boston University)

16:00 Poster session

Do., 17. April ¶

25 TBA¶

TBA

Sprecher: Prof. Zhen-Sheng Yuan (USTC)

26 Studying (doped) magnets using arrays of Rydberg atoms¶

In this talk, I will present our recent studies of quantum magnetism using a Rydberg quantum simulator. I will first explain how, using two different Rydberg levels such as nS and nP, we can study the equilibrium properties and the dynamics of dipolar XY magnets, in one [1] and two dimensions [2,3]. I will then show that by using three Rydberg states, nS, nP, and n’S, one can realize a bosonic version of the t-J model that describes doped magnet [4].
[1] Gabriel Emperauger et al., Tomonaga-Luttinger Liquid Behavior in a Rydberg-encoded Spin Chain, arXiv:2501.08179.
[2] C. Cheng et al., Continuous Symmetry Breaking in a Two-dimensional Rydberg Array, Nature 616, 691 (2023).
[3] C. Cheng et al., Spectroscopy of elementary excitations from quench dynamics in a dipolar XY Rydberg simulator, arXiv:2311.11726
[4] Mu Qiao et al., Realization of a doped quantum antiferromagnet with dipolar tunnelings in a Rydberg tweezer array, arXiv:2501.08233.

Sprecher: Dr. Thierry Lahaye (Institut d'Optique)

10:30 Coffee break

27 Absence of localization in interacting spin chains with a discrete symmetry¶

In this talk, I will present a proof of delocalization in spin chains symmetric under a combination of mirror and spin-flip symmetries and with a nondegenerate spectrum. The proof applies to two prominent examples: the Stark many-body localization system (Stark-MBL) and the symmetrized many-body localization system (symmetrized–MBL). I will also provide numerical evidence of delocalization at all energy densities in these models and show that the delocalization mechanism appears robust to weak symmetry breaking.

Sprecher: Prof. Yevgeny Bar Lev (Ben Gurion University of the Negev)

28 Quantum many-body scars beyond the PXP model in Rydberg simulators¶

Persistent revivals recently observed in Rydberg atom arrays have challenged our understanding of thermalisation and attracted much interest to the concept of quantum many-body scarring : the presence of coherent dynamics in otherwise chaotic Hamiltonians. They have since been reported in multiple models, including the kinetically-constrained PXP model realised in Rydberg chains. At the same time, questions of how common scarring is and in what systems it can be observed remain open. In particular, decreasing the spacing between Rydberg atoms to make the constraint act beyond nearest-neighbours seemingly destroys scarring.
In this talk, I will discuss how this breakdown of scarring can be understood through the lens of frustration linked to the constraint. Crucially, this frustration can be lifted by entanglement, making it possible to witness coherent oscillations for an arbitrary constraint range. However, in contrast to the PXP model, their observation requires launching dynamics from weakly entangled initial states rather than from a product state. This key insight allows us to demonstrate that scarring exists in a much broader family of experimentally-realisable models that includes and generalises PXP to longer-range constraints and states with different periodicity. Our approach can also be used in higher dimensions where frustration is more ubiquitous, revealing a plethora of new scarred trajectories.

Sprecher: Dr. Jean-Yves Desaules (ISTA)

12:00 Lunch

29 A photon-coupled atomic tweezer array¶

Photon-mediated interactions are a powerful tool for realizing multi-particle entanglement and long-range interacting Hamiltonians. They have been studied both in systems with collectively coupled atomic ensembles, and with strongly coupled few-body systems. However, creating photon-mediated interactions in larger systems with single-atom control remains challenging. We report on experiments with an atomic tweezer array that is coupled to an optical fiber cavity. The setup combines single-atom control with photon-mediated interactions in the strong coupling regime, and it includes a real-time measurement channel through the optical fiber. This opens a path for programmable interactions within an atomic tweezer array, for non-destructive readout protocols, and to implement dissipative state preparation schemes.

Sprecher: Prof. Julian Leonard (ISTA)

30 Building Error-Corrected Quantum Computers With Neutral Atom Qubits¶

Neutral-atom qubits offer a promising platform for fault-tolerant quantum computing. We demonstrate a quantum computer—featuring 100s of atomic qubits, a universal gateset, and qubit movement—performing error correction and computation on 24-28 logical qubits.

Sprecher: Dr. Mark Stone (Atom Computing)

14:30 Coffee break

31 Entanglement dynamics from universal low-lying modes¶

Information-theoretic quantities, such as Rényi entropies, exhibit remarkable universality in their late-time behavior across a wide range of chaotic quantum many-body systems. Understanding how these common features arise from vastly different microscopic dynamics remains an important challenge. In this talk, I will show this mechanism for a class of one-dimensional Brownian models with random, time-dependent Hamiltonians and a variety of microscopic couplings. In these models, the real-time Lorentzian evolution of the n-th Rényi entropy can be mapped onto an imaginary time Euclidean evolution of an effective Hamiltonian acting on 2n copies of the system. In the absence of symmetries, the ground states of this effective Hamiltonian resemble ferromagnets, hence its low-energy excitations are gapped domain walls between these ferromagnetic ground states. I will demonstrate how the membrane picture of entanglement growth naturally emerges from the physics of these domain-wall excitations, and show that the membrane tension is determined by their dispersion relation. While this prescription works straightforwardly for the computation of the membrane tension for the second Rényi entropy, there are subtleties that arise for higher Rényi entropies, which I will discuss. In all, this framework provides a universal understanding of entanglement dynamics in one dimension in terms of gapped low-lying modes, with potential extensions to non-random systems governed by time-independent Hamiltonians. Finally, I will discuss the fate of this picture in the presence of measurements, symmetries, and in higher-dimensional settings.

Sprecher: Dr. Sanjay Moudgalya (TUM)

32 Coarsening dynamics on a Rydberg quantum simulator¶

Understanding the out-of-equilibrium dynamics of a closed quantum system driven across a quantum phase transition is an important problem with widespread implications for quantum state preparation and adiabatic algorithms. While the quantum Kibble-Zurek mechanism elucidates part of these dynamics, the subsequent and significant coarsening processes lie beyond its scope. Here, we develop a universal description of such coarsening dynamics---and their interplay with the Kibble-Zurek mechanism---in terms of scaling theories. Our comprehensive theoretical framework applies to a diverse set of ramp protocols and encompasses various coarsening scenarios involving both quantum and thermal fluctuations. Moreover, we highlight how such coarsening dynamics can be directly studied in today's "synthetic" quantum many-body systems, including Rydberg atom arrays, and present detailed results on the experimental observation of such collective dynamics across a (2+1)D Ising quantum phase transition.

Sprecher: Dr. Rhine Samajdar (Princeton University)