Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N33: NonEquilibrium Physics with Cold Atoms and Molecules, Rydberg Gases, and Trapped Ions IIFocus Recordings Available

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Sponsoring Units: DAMOP DCMP Chair: Steve Campbell, University College Dublin Room: McCormick Place W192C 
Wednesday, March 16, 2022 11:30AM  11:42AM 
N33.00001: Observing emergent hydrodynamics in a longrange quantum magnet Alexander Schuckert, Manoj K Joshi, Florian Kranzl, Izabella Lovas, Christine Maier, Rainer Blatt, Michael Knap, Christian Roos Identifying universal properties of nonequilibrium quantum states is a major challenge in modern physics. A fascinating prediction is that classical hydrodynamics emerges universally in the evolution of any interacting quantum system. We study the dynamics of a longrange interacting spin system with nonequilibrium quantum field theory, predicting the emergence of a whole family of hydrodynamic universality classes, ranging from normal diffusion to anomalous superdiffusion. We experimentally test these predictions in the quantum dynamics of 51 individually controlled ions. By measuring spacetime resolved correlation functions in an infinite temperature state, we observe the emergence of hydrodynamics at late time. We extract the transport coefficients of the hydrodynamic theory, reflecting the microscopic properties of the system. Our observations demonstrate the potential for engineered quantum systems to provide key insights into universal properties of nonequilibrium states of quantum matter and uncover the transport processes governing longrange interacting systems. 
Wednesday, March 16, 2022 11:42AM  11:54AM 
N33.00002: Probing the edge between integrability and quantum chaos in interacting fewatom systems Thomás Fogarty, Miguel A GarciaMarch, Lea F Santos, Nathan L Harshman Interacting quantum systems in the chaotic domain are at the core of various ongoing studies of manybody physics, ranging from the scrambling of quantum information to the onset of thermalization. We propose a minimum model for chaos that can be experimentally realized with cold atoms trapped in onedimensional multiwell potentials. We explore the emergence of chaos as the number of particles is increased, starting with as few as two, and as the number of wells is increased, ranging from a double well to a multiwell KronigPenneylike system. In this way, we illuminate the narrow boundary between integrability and chaos in a highly tunable fewbody system. We show that the competition between the particle interactions and the periodic structure of the confining potential reveals subtle indications of quantum chaos for 3 particles, while for 4 particles stronger signatures are seen. The analysis is performed for bosonic particles and could also be extended to distinguishable fermions. 
Wednesday, March 16, 2022 11:54AM  12:06PM 
N33.00003: Optimizing Rydberg Antennas Peter B Weichman Given their low electromagnetic profile, specially prepared atomic Rydberg vapors have already demonstrated improvement over conventional wire antennas as calibration standards for electric field measurements. Major efforts are now under way to develop practical room temperature Rydberg atom RF receivers with greater sensitivity, bandwidth, and dynamic range than any classical receiver. In this presentation I will summarize theoretical analysis of various laser and RF local oscillator setups, with the goal of optimizing the underlying electromagnetic transparency (EIT) sensitivity against environmental noise, atomic motioninduced Doppler, RF communication signal waveform, and other important effects. At the heart of the analysis is a carefully controlled resonant coupling of the low energy core and highly excited Rydberg atomic level subspaces. The incident RF signal perturbation of the Rydberg state amplitudes then induces a corresponding large perturbation of the core state amplitudes. This nonequilibrium multistate entanglement is enabled by an effective Hamiltonian eigenvalue neardegeneracy whose avoided crossing produces the required extreme sensitivity. This formulation of the problem enables a very efficient method for optimizing various proposed experimental setup designs. 
Wednesday, March 16, 2022 12:06PM  12:18PM 
N33.00004: Strongly interacting two photon random walk in an array of single atom beamsplitters xinyuan zheng, Edo Waks Few photon quantum walk is a powerful tool for quantum simulation. However, most theoretical and experimental works related to this topic have been focused on linear beam splitter arrays, which lack photonphoton interactions. Here we propose a novel way of implementing a strongly interacting two photon discrete time quantum walk. We use single atom beam splitters to induce strong photonphoton interaction. Photonic quantum walks in such a nonlinear beam splitter array are still poorly understood. In this work, we theoretically investigated the two photon correlation functions at the output and observed strong photonphoton interaction which yield various types of photon statistics. Finally, we propose a practical realization of our random walk based on timemultiplexed synthetic dimensions. Our proposal has opened the door for a novel approach of quantum simulation using photons. 
Wednesday, March 16, 2022 12:18PM  12:30PM 
N33.00005: Anisotropic sound propagation in dilute dipolar gases. Reuben R Wang, John L Bohn Ultracold dipolar gases have garnered extensive interest in recent years, attributed to their capacity for a rich variety of dynamical phenomena. One such instance is anisotropic scattering, dominant in thermal dipolar gases in the quantum collision regime. When taken out of equilibrium, this anisotropy can lead to axially differentiated spreading of energy through the gas. To this end, we study how dipolar collisions lead to an anisotropic viscosity that distorts acoustic wave propagation. The implications to diffusive transport are addressed, and extensions to this work are proposed. Analysis is performed with a semianalytic theory based on the Enskog formalism, verified by numerical Monte Carlo simulations. This work is funded by the NSF. 
Wednesday, March 16, 2022 12:30PM  12:42PM 
N33.00006: Thermalization dynamics of a U(1) lattice gauge theory on a BoseHubbard quantum simulator GuoXian Su, Zhaoyu Zhou, Jad C Halimeh, Robert Ott, Hui Sun, Philipp Hauke, Bing Yang, Zhensheng Yuan, Jürgen Berges, JianWei Pan Gauge theories form the foundation of modern physics, with applications ranging from elementary particle physics and earlyuniverse cosmology to condensed matter systems. We demonstrate the emergence of irreversible thermal equilibrium behavior for farfromequilibrium gauge field, by quantum simulating the fundamental unitary dynamics of a U(1) symmetric gauge field theory. While this is in general beyond the capabilities of classical computers, it is made possible through the experimental implementation of a 71site cold atomic system in an optical superlattice. The highly constrained gauge theory dynamics is encoded in a onedimensional BoseHubbard simulator, which couples fermionic matter fields through dynamical gauge fields. We investigate the farfromequilibrium evolution and the equilibration to a steady state well approximated by a thermal ensemble. Our work establishes a new realm for the investigation of elusive phenomena, such as Schwinger pair production and stringbreaking, and paves the way for more complex higherdimensional gauge theories on quantum synthetic matter devices. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N33.00007: Ferromagnetism in tilted fermionic Mott insulators Masaki Tezuka, Kazuaki Takasan We investigate the magnetism of tilted fermionic Mott insulators. With a small tilt, the fermions are almost localized and still form a Mottinsulating state, where the localized spins interact with each other via antiferromagnetic exchange coupling modified by the tilt [1,2]. A large tilt, rather than destroying localization, induces the WannierStark localization and the fermions can still be regarded as a localized spin system. The sign of the exchange coupling can be changed to realize ferromagnetic interaction. We show these behaviors via both perturbation theory and realtime numerical simulation for the fermionic Hubbard chain. Our simulation shows that it is possible to effectively control the speed and timedirection of the realtime dynamics with the tilt. 
Wednesday, March 16, 2022 12:54PM  1:30PM 
N33.00008: Valley Prize (2022): TBD Invited Speaker: Andrew Lucas I will describe new universality classes of hydrodynamic phenomena and nonequilibrium fixed points which arise in constrained manybody systems. These new theories are inspired by exotic physical systems with "fracton" excitations. I will highlight how modern methods from effective field theory are leading us to a systematic understanding and classification of new universality classes of constrained hydrodynamics and how  in turn  these new fluids might lead us to a better understanding of hydrodynamics more generally. 
Wednesday, March 16, 2022 1:30PM  1:42PM 
N33.00009: Continuous time crystal from a spontaneous manybody Floquet state Fernando Sols, J. R. M. de Nova

Wednesday, March 16, 2022 1:42PM  1:54PM 
N33.00010: Emergence of Hilbert Space Fragmentation in the Ising Model with a Weak Transverse Field Atsuki Yoshinaga, Takashi Imoto, Hideaki Hakoshima, Yuichiro Matsuzaki, Ryusuke Hamazaki The last two decades have witnessed a substantial advance in revealing conditions for quantum manybody systems to thermalize following the experimental progress in quantum simulators. The transversefield Ising model is one of the fundamental models in quantum manybody systems, yet full understanding of its dynamics remains elusive for higher than in one dimension. Here, we show the emergence of nonergodicity for the Ising model in a weak transverse field on a square lattice in arbitrary dimension d. Specifically we investigate the effective nonintegrable model in the weaktransverse field limit and demonstrate that novel Hilbertspace fragmentation occurs for d>1 as a consequence of only one emergent U(1) conservation law, i.e., domainwallnumber conservation. This conservation law leads to a kinetic constraint in the model and the appearance of frozen regions, which give rise to exponentially many fragmented subspaces in the Hilbert space. Our results indicate nontrivial initialstate dependence for longlived prethermal dynamics of the Ising models in a weak transverse field. 
Wednesday, March 16, 2022 1:54PM  2:06PM 
N33.00011: Quench dynamics of 2D Bose gases across the BKT critical point Shinichi Sunami, David Garrick, Abel Beregi, Elliot Bentine, Christopher J Foot We report on the observation of nonequilibrium dynamics in 2D quantum systems across a critical point. We quench the system by coherently splitting a single 2D Bose gas into two, resulting in the dynamical crossing of the BerezinskiiKosterlitzThouless phase transition. We monitor the relaxation dynamics towards the vortexproliferated disordered phase using a matterwave interferometry technique and find the time evolution of the phase correlation function and vortex density. We identify that the temporal decay of the correlation is related to the energy scale associated with vortex excitations. We further compare measured vortex unbinding dynamics with the realtime renormalisation group theory. 
Wednesday, March 16, 2022 2:06PM  2:18PM 
N33.00012: Finite speed of quantum information in models of interacting bosons at finite density Chao Yin, Andrew Lucas We prove that quantum information propagates with a finite velocity in any model of interacting bosons whose (possibly timedependent) Hamiltonian contains spatially local singleboson hopping terms along with arbitrary local densitydependent interactions. More precisely, with density matrix ρ∝exp[μN] (with N the total boson number), ensemble averaged correlators of the form 〈[A_{0} ,B_{r} (t)]〉, along with outoftimeordered correlators, must vanish as the distance r between two local operators grows, unless t≥r/v for some finite speed v. In one dimensional models, we give a useful extension of this result that demonstrates the smallness of all matrix elements of the commutator [A_{0} ,B_{r} (t)] between finite density states if t/r is sufficiently small. Our bounds are relevant for physically realistic initial conditions in experimentally realized models of interacting bosons. In particular, we prove that v can scale no faster than linear in number density in the BoseHubbard model: this scaling matches previous results in the high density limit. The quantum walk formalism underlying our proof provides an alternative method for bounding quantum dynamics in models with unbounded operators and infinitedimensional Hilbert spaces, where LiebRobinson bounds have been notoriously challenging to prove. 
Wednesday, March 16, 2022 2:18PM  2:30PM 
N33.00013: Nonequilibrium HanburyBrownTwiss experiment: Theory and application to binary stars Adrian E Rubio Lopez, Fanglin Bao, Ashwin K Boddeti, Hyunsoo Choi, Zubin Jacob In this work we consider the HanburyBrown and Twiss experiment for a configuration of two extended objects at different temperature. We show that intensity interference for these scenarios appears as an alternative method for measuring the features of the binary system. Unlike the case of equilibrium scenarios or the twophoton states, both temperatures and radii of each object take a role on the photon correlations. In addition to the interference oscillations on the secondorder coherence, a longbaseline asymptotic value shows to depend on the observation frequency, temperatures and radii of both objects. We discuss the advantages of measuring each magnitude and also its combination according to the experimental possibilities. By finally including some aspects of the orbital motion to our approach, we apply it to the case of binary stars (in particular, Luhman 16 and Spica α Vir systems), showing that the method might be suitable for estimating not only the radii but the temperatures of the constituents. For the case of the Luhman 16 we show that measuring both magnitudes should be possible in the visible range with baselines of no more than hundreds of meters, while for the case of the Spica the same is possible in the ultraviolet regime but with baselines of tenths of meters. We believe that our work contributes to improve both fundamental and practical aspects of intensity interferometry as a tool for characterizing binary systems. 
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