
Chair: Matthew Wampler

09:00  09:35

Arnab Das
(Indian Association for the Cultivation of Science)
Dynamical Freezing and Energy Unprotected Emergent Conservation Laws
Dynamical freezing refers to the phenomenon of perpetual but approximate freezing or conservation of certain local operators close to their initial values in a generic, disorderfree, quantum chaotic manybody system, under strong periodic drive. These conservation laws are "emergent", as they are not respected in the undriven system. This is a way to evade Thermalization at late times in the absence of disorder even in the thermodynamic system. We will conjecture a recipe for constructing the conservation laws and show that they are not necessarily protected by high energy costs that can be posed by the strong drive field. This provides a new route to stabilizing and engineering interacting quantum matter far from equilibrium, and also help quantum state preservation. It also raises new questions regarding mechanisms of stabilizing quantum of matter out of equilibrium, and formulating Statistical Mechanics with approximate but perpetual constraints.

09:35  10:10

Eduard Jürgen Braun
(University of Heidelberg)
Observation of hysteresis in a disordered dipolar Heisenberg spin system
The interplay between disorder and magnetic frustration in spin glasses keeps remaining one of the most prominent unsolved problems in statistical physics, with important applications in optimization, quantum annealing, and the fundamental research interest in the study of thermalization and ergodicity. An important subclass of these systems are dipolar interacting ones, where the existence of a spin glass phase in the strong diluted regime has been controversial over decades.
In this talk, I will present two new protocols that we developed in order to characterize hysteresis, and possibly replica symmetry breaking, in an isolated dipolar system, which we realize on a Rydberg atom quantum simulation platform, where the spin degree of freedom is encoded in two different Rydberg states. Complementing other techniques that rely on a full measurement of the spin glass overlap, our techniques involve only global state preparation and measurements. The techniques show hysteresis both in a few particle finite size simulation as well as in a mesoscopic quantum simulation, giving a first indication of a possible quantum phase transition and replica symmetry breaking in a disordered dipolar Heisenberg spin system with a transverse field.

10:10  10:35

Ilya Esin
(CALTECH)
Quantized Acoustoelectric Floquet Effect in Quantum Nanowires
External coherent fields can drive quantum materials into nonequilibrium states, revealing exotic properties that are unattainable under equilibrium conditions  an approach known as "Floquet engineering." While optical lasers have commonly been used as the driving fields, recent advancements have introduced nontraditional sources, such as coherent phonon drives. Building on this progress, we demonstrate that driving a metallic quantum nanowire with a coherent wave of terahertz phonons can induce an electronic steady state characterized by a persistent quantized current along the wire. The quantization of the current is achieved due to the coupling of electrons to the nanowire's vibrational modes, providing the lowtemperature heat bath and energy relaxation mechanisms. Our findings underscore the potential of using nonoptical drives, such as coherent phonon sources, to induce nonequilibrium phenomena in materials. Furthermore, our approach suggests a new method for the highprecision detection of coherent phonon oscillations via transport measurements.

10:35  11:05

coffee break

11:05  11:40

David Long
(University of Maryland)
Anomalous localized topological phases
There is a wellestablished principle and formalism for classifying ground state phases of gapped Hamiltonian systems  Hamiltonians which can be deformed into one another without closing the gap belong to the same topological phase. In the nonequilibrium context, topological phases of localized systems may be identified as sets of Hamiltonians which can be deformed into one another without going through a delocalization transition. For Floquet systems, it is known how to map the classification of such phases to a classification of locality preserving unitaries  called quantum cellular automata (QCA)  which characterize dynamics at the boundary of a sample. We show how to classify localized topological phases using QCAs beyond the context of periodic driving, including static and quasiperiodically driven systems. Further, we adapt many tools from the study of gapped ground states to the localized context, allowing for significant progress in the classification. Some of the localized topological phases so discovered are characterized by eigenstate order  eigenstates of the model are ordered like ground states of nontrivial gapped Hamiltonians. However, there are also anomalous localized topological phases (ALT phases), for which each eigenstate is trivial when regarded individually, but the system as a whole still cannot be deformed into an atomic insulator.

11:40  12:15

Ion Cosma Fulga
(Leibniz Institute for Solid State and Materials Research Dresden)
Noise resilience of the anomalous FloquetAnderson insulator
We study the effect of noise on twodimensional periodically driven topological phases, focusing on two examples: the anomalous FloquetAnderson insulator and the disordered FloquetChern insulator. We show that the former is substantially more robust against temporal noise than the latter, i.e. its initially populated topological modes undergo an algebraic decay as a function of time, instead of an exponential one. Using a combination of analytical results, phenomenological models, as well as fullscale numerical simulations, we find that this additional diffusive regime occurs at intermediate times, and that it is absent in the FloquetChern insulator, where the decay remains exponential throughout. Surprisingly, this is a consequence of a thermalization that occurs specifically among edge modes, separate from the bulk. Our findings indicate that anomalous phases, instead of Chern phases, are ideal candidates for potential applications of Floquet topology, given the unavoidable presence of both quenched disorder and decoherence in experiments.

12:15  14:00

lunch break


Chair: Iliya Esin

14:00  14:35

Markus Heyl
(Universität Augsburg)
Active quantum flocks
Flocks of animals represent a fascinating archetype of collective behavior in the macroscopic classical world, where the constituents, such as birds, concertedly perform motions and actions as if being one single entity. Here, we address the outstanding question of whether flocks can also form in the microscopic world at the quantum level. For that purpose, we introduce the concept of active quantum matter by formulating a class of models of active quantum particles on a onedimensional lattice. We provide both analytical and largescale numerical evidence that these systems can give rise to quantum flocks. A key finding is that these flocks, unlike classical ones, exhibit distinct quantum properties by developing strong quantum coherence over long distances. We propose that quantum flocks could be experimentally observed in Rydberg atom arrays. Our work paves the way towards realizing the intriguing collective behaviors of biological active particles in quantum matter systems. We expect that this opens up a path towards a yet totally unexplored class of nonequilibrium quantum manybody systems with unique properties.

14:35  15:00

Kazuaki Takasan
(University of Tokyo)
Activityinduced quantum phase transitions: A proposal for quantum active matter
Active matter is an ensemble of selfpropelled entities, such as flocks of birds and schools of fish, that has attracted much attention for its various phase transitions and pattern formations that are not present in equilibrium systems [1]. While the physics of active matter has been studied extensively in statistical physics and biophysics, most studies have been limited to classical systems, and the possibility of active matter in quantum systems has rarely been considered. However, recent developments in atomicmolecularoptical systems allow us to study the complex dynamics of quantum manybody systems in a highly controlled manner, and it may be possible to design quantum manybody systems that behave like active matter. Stimulated by this, the study of the quantum analog of active matter has been initiated very recently [26]. In particular, we have studied quantum phase transitions analogous to the nonequilibrium phase transitions of active matter [2,6].
In this presentation, we would like to present our work on quantum active matter. We have studied twocomponent (spin1/2) hardcore bosons with spindependent asymmetric hopping corresponding to the motility of each active particle. This is expected to be realized with ultracold atoms with a dissipative optical lattice. We have shown that this model can be regarded as a quantum generalization of classical active matter models defined on a lattice, and that it exhibits various phase transitions, including nonequilibrium phase transitions unique to active matter, such as motilityinduced phase separation [2]. In more recent work [6], we have shown that the combination of activity and repulsive interaction induces ferromangnetism, based on both numerical and analytical arguments. This activityinduced ferromangnetism can be considered as a quantum counterpart of flocking. While the flocking transition in classical systems requires a microscopic alignment interaction, this mechanism does not require such an interaction and thus may be unique to quantum active matter. We believe that our works extending active matter physics to quantum systems help to broaden the perspective on nonequilibrium phases of matter beyond conventional paradigms.
[1] M. C. Marchetti et al., Rev. Mod. Phys. 85, 1143 (2013).
[2] K. Adachi, KT, K. Kawaguchi, Phys. Rev. Research 4, 013194 (2022).
[3] M. Yamagishi, N. Hatano, H. Obuse, arXiv: 2305.15319
[4] Y. Zheng, B. Liebchen, H. Löwen, arXiv: 2305.16131
[5] R. Khasseh, S. Wald, R. Moessner, C. A. Weber, M. Heyl, arXiv: 2308.01603
[6] KT*, K. Adachi*, K. Kawaguchi, Phys. Rev. Research 6, 023096 (2024). (*equally contributed)

15:00  15:30

coffee break

15:30  16:05

Wen Wei Ho
(National University of Singapore)
Deep thermalization and generalized maximum entropy principles
Thermalization in a closed quantum system is defined by the dynamical approach of local observables toward universal expectation values, computed within a thermal Gibbs state. In this talk, I want to explain how a more refined notion of quantum equilibration can be studied by resolving the local state of a system via conditioning it on measurements of the complement (the “bath”). This yields an ensemble of pure conditional states — representing a physically motivated unraveling of the reduced density matrix — which describes a wavefunction distribution over the Hilbert space. I will show that for generic complex quantum dynamics, the ensemble tends toward universal distributions constrained only by global conservation laws, a process we dub "deep thermalization". Underpinning this phenomenon is a generalized maximum principle, which endows the limiting ensembles with the special quantum informationtheoretic property of possessing minimal accessible information. I will show how this principle applies across physically distinct systems of discretevariable spin systems as well as continuousvariable bosonic Gaussian systems. Our results demonstrate the power of quantum information theoretic frameworks in unveiling new physical phenomena and principles in quantum dynamics and statistical mechanics.

16:05  16:30

Daniel Mark
(MIT)
Universal randomness in quantum ergodic dynamics: Benchmarking, noise learning and beyond
We discuss universal fluctuations that arise from natural quantum manybody dynamics. These fluctuations are unique to the statistics of global bitstring measurements and have been used in random circuit sampling tasks for recent quantum advantage claims. Based on such fluctuations, I will introduce a sampleefficient protocol which estimates the fidelity between an experimentally prepared state and an ideal target state, and is applicable to a wide class of analog quantum simulators. Finally, we apply this protocol in a 60atom analog Rydberg quantum simulator, and further use our results to quantify the amount of mixed state entanglement present, as well as learning about the noise. We find that the experiment is competitive in this respect with stateoftheart digital quantum devices performing random circuit evolution and we distinguish the proportion of local vs. global noise in the system.

16:30  17:05

Soonwon Choi
(MIT)
Complete HilbertSpace Ergodicity in Quantum Dynamics (remote)
Ergodicity of quantum dynamics is often defined through statistical properties of energy eigenstates, as exemplified by Berry’s conjecture in singleparticle quantum chaos and the eigenstate thermalization hypothesis in manybody settings. Then, how can we define the ergodicity for quantum dynamics for which the notion of eigenstates does not exist? In this work, we introduce an alternative, stronger form of ergodicity, wherein any timeevolved state uniformly visits the entire Hilbert space over time. Such a phenomenon, called complete Hilbertspace ergodicity (CHSE) is more akin to the intuitive notion of ergodicity as an inherently dynamical concept. CHSE cannot hold for timeindependent or even timeperiodic Hamiltonian dynamics, owing to the existence of (quasi)energy eigenstates. However, we show that there exists a family of aperiodic, yet deterministic drives with minimal symbolic complexity — generated by the Fibonacci word and its generalizations — for which CHSE can be proven to occur. These results provide a basis for understanding thermalization in general timedependent quantum systems.
Based onPhys. Rev. Lett. 131, 250401 (2023)

17:05  17:30

break

17:30  18:00

poster flash session I (odd poster numbers)

18:00  19:00

dinner

19:00

poster session I
(focus on odd poster numbers)
