Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D50: Universal Dynamics near Phase TransitionsRecordings Available

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Sponsoring Units: DCMP Chair: Justin Song, Nanyang University Room: McCormick Place W474A 
Monday, March 14, 2022 3:00PM  3:12PM 
D50.00001: Probing Equilibrium and Dynamical Criticality Through Spatially Minimal Measurements Ceren B Dag, Philipp J Uhrich, Jad C Halimeh Extracting critical behavior in the wake of quantum quenches, with particular emphasis on experimental feasibility, has recently been at the forefront of theoretical and experimental investigations in condensed matter physics and quantum synthetic matter (QSM). Here, we investigate the potential of spatially minimal measurements, in the form of singlesite observables, for probing equilibrium phase transitions and dynamical criticality in the transversefield Ising chains (TFIC) with hard boundaries. For integrable and nearintegrable TFIC, our exact and meanfieldtheory analyses reveal a truly outofequilibrium universal scaling exponent $\beta\sim 4/3$ in the vicinity of the transition. We demonstrate the robustness of this exponent with respect to the initial state, as well as the location of the probe site. We extend our analyses to strongly nonintegrable TFIC, with longrange powerlaw or nextnearestneighbor interactions, using tDMRG calculations. Both finitesize and finitetime analyses suggest a dynamical critical point for the strongly nonintegrable and locally connected TFIC. Our work provides a robust scheme for the experimental detection of quantum critical points and dynamical scaling laws in shortrange interacting models. 
Monday, March 14, 2022 3:12PM  3:24PM 
D50.00002: Quantum Criticality Using a Superconducting Quantum Processor Maxime Dupont, Joel E Moore Quantum criticality emerges from the collective behavior of many interacting quantum particles, often at the transition between different phases of matter. It is one of the cornerstones of condensed matter physics, which we access on noisy intermediatescale (NISQ) quantum devices by leveraging a dynamicallydriven phenomenon. We probe the critical properties of the onedimensional quantum Ising model on a programmable superconducting quantum chip via a KibbleZurek process, obtain scaling laws, and estimate critical exponents despite inherent sources of errors on the hardware. A oneparameter noise model captures the effect of imperfections and reproduces the experimental data. Its systematic study reveals that the noise, analogously to temperature, induces a new length scale in the system. We introduce and successfully verify modified scaling laws, directly accounting for the noise without any prior knowledge, enhancing the power of NISQ processors considerably for addressing quantum criticality and potentially other phenomena and algorithms. 
Monday, March 14, 2022 3:24PM  3:36PM 
D50.00003: PostQuantum Quench Growth of Renyi Entropies in Perturbed Luttinger Liquids Robert M Konik, Pasquale Calabrese, Sara Murciano The growth of Renyi entropies after the injection of energy into a correlated system provides a window upon the dynamics of its entanglement properties. We provide here a scheme by which this growth can be determined in Luttinger liquids systems with arbitrary interactions, even those introducing gaps into the liquid. This scheme introduces the notion of a generalized mixed state Renyi entropy. We show that these generalized Renyi entropies can be computed and provide analytic expressions thereof. Using these generalized Renyi entropies, we provide analytic expressions for the short time growth of the second and third Renyi entropy after a quantum quench of the coupling strength between two Luttinger liquids, relevant for the study of the dynamics of cold atomic systems. For longer times, we use truncated spectrum methods to evaluate the postquench Renyi entropy growth. 
Monday, March 14, 2022 3:36PM  3:48PM 
D50.00004: Hidden quantum criticality in quench dynamics of the XY model Sanku Paul, Paraj Titum, Mohammad Maghrebi We investigate the stationary states of the onedimensional anisotropic XY model upon a sudden quench. We find that quenches along the critical line display surprising behavior: While the longtime stationary state shows a typical volumelaw entanglement and exponential decay of twopoint correlations, a subleading logarithmic term emerges indicating that mutual information is critical. We find the same behavior in logarithmic negativity, indicating quantum criticality yet at finite energy density. We attribute this behavior to the vanishing effective temperature of the soft mode in spite of the quench. Finally, we discuss experimental platforms where this physics can be observed experimentally. 
Monday, March 14, 2022 3:48PM  4:00PM 
D50.00005: Finite Entanglement Scaling of a KibbleZurek sweep in the Transverse Field Ising Model Nicholas E Sherman, Aleksandr Avdoshkin, Joel E Moore Quantum criticality harbors universal physics with observables near a quantum critical point (QCP). Such points in 1D are usually constrained by conformal symmetry, thus vastly reducing the number of parameters needed to describe the system. Although conformal symmetry provides immense simplifications analytically, the presence of logarithmic corrections to the entanglement entropy makes QCPs challenging to probe numerically. As conjectured in the finite entanglement scaling hypothesis (FES), using an MPS with a finite bonddimension introduces a length scale into the system, spoiling the conformal symmetry. However, a careful scaling analysis in the bonddimension can extract insights about the nature of quantum critical points. Furthermore, performing time evolution with a time dependent Hamiltonian that continuously travels through a QCP leads to excitation production, via the KibbleZurek (KZ) mechanism, and introduces a length scale into the problem determined by the rate v at which the Hamiltonian is changed. Deviations from the quantum critical properties are fully determined by v, and the critical exponents of the QCP. In this work, we find that observables reproduce the KZ predictions, but are modulated by a scaling function of the ratio of the two length scales. Moreover, we find that the length scale introduced by finite bonddimension in KZ dynamics is the same length scale conjectured by the FES. 
Monday, March 14, 2022 4:00PM  4:12PM 
D50.00006: Emergent eigenstate solution for generalized thermalization Yicheng Zhang, Lev Vidmar, Marcos Rigol Generalized thermalization is a process that occurs in integrable systems in which unitary dynamics, e.g., following a quantum quench, results in states in which observables after equilibration are described by generalized Gibbs ensembles (GGEs). Here we discuss an emergent eigenstate construction that allows one to build emergent local Hamiltonians of which one eigenstate captures the entire generalized thermalization process following a global quantum quench. Specifically, we study the emergent eigenstate that describes the quantum dynamics of hardcore bosons in one dimension (1D) for which the initial state is a density wave, and this state evolves under a homogeneous Hamiltonian. 
Monday, March 14, 2022 4:12PM  4:24PM 
D50.00007: Beyond the KibbleZurek mechanism  Universal distribution of topological defects created across a phase transition Fernando J GomezRuiz, Jack J Mayo, Zhi H Li, Chuan Y Xia, Hua B Zeng, Hai Q Zhang, Adolfo del Campo Nonequilibrium phenomena occupy a prominent role at the frontiers of physics. Since its conception in the mid70s, the KibbleZurek mechanism (KZM) has been the paradigmatic framework to describe the dynamics of phase transition, in which symmetry breaking leads to the formation of topological defects (e.g. vortices in a superfluid or kinks in a spin chain). Its key testable prediction is that the average number of topological defects scales as a universal power law with the quench rate (ie. the velocity at which the critical point is crossed). The authors unveil signatures of universality beyond the mean number of topological defects and show that the full counting statistics of topological defects is actually unanimous. In particular, the authors show that i) the defect number distribution is binomial, ii) all cumulants are proportional to the mean and scale as a universal power law with the quench rate, iii) this power law is fixed by the KZM scaling. This knowledge allows one to characterize universal features regarding the onset of adiabatic dynamics (probability for no defects) and large deviations of the number of kinks away from the mean value. This prediction is experimentally testable in the wide range of tangible platforms in which the KZM has been studied: trapped ion chains, liquid crystals, BoseEinstein Condensate clouds, colloidal monolayers, to name just a few instances. The authors' findings provide a comprehensive set of predictions that can be subjected to extensive theoretical/numerical/experimental verification and apply to various disciplines and experimental systems. 
Monday, March 14, 2022 4:24PM  4:36PM 
D50.00008: KibbleZurek mechanism in the Ising Field Theory Kristóf Hódsági, Marton Kormos, Gábor Takács, Dávid X Horváth How can we describe the formation of order in critical systems? If we tune the control parameters such that the system crosses the critical point, the answer is given by the KibbleZurek mechanism (KZM) that predicts universal dependence of observables on the rate of change of the control parameter. In recent years the KZM has been generalized to the context of quantum criticality. Our recent work explores the KZM in the Ising Field Theory, where the quantum critical point can be crossed in different directions in the twodimensional coupling space leading to different scaling laws. We investigate the dynamics in this genuinely interacting field theory using a recently developed version of the Truncated Conformal Space Approach. We demonstrate dynamical scaling in the nonadiabatic time window and provide analytic and numerical evidence for specific scaling properties of various quantities. In particular, we argue that for a slow enough ramp, the higher cumulants of the excess heat exhibit universal scaling in generic interacting models. 
Monday, March 14, 2022 4:36PM  4:48PM 
D50.00009: Quantum phase transition dynamics in the twodimensional transversefield Ising model Markus Schmitt, Marek M Rams, Jacek Dziarmaga, Markus Heyl, Wojciech H Zurek The quantum KibbleZurek mechanism (QKZM) predicts universal dynamical behavior in the vicinity of quantum phase transitions (QPTs). It is now well understood for onedimensional quantum matter. Higherdimensional systems, however, remain a challenge, complicated by fundamental differences of the associated QPTs and their underlying conformal field theories. In this work, we take the first steps towards exploring the QKZM in two dimensions. We study the dynamical crossing of the QPT in the paradigmatic Ising model by a joint effort of modern stateoftheart numerical methods. As a central result, we quantify universal QKZM behavior close to the QPT. However, upon traversing further into the ferromagnetic regime, we observe deviations from the QKZM prediction. We explain the observed behavior by proposing an extended QKZM taking into account spectral information as well as phase ordering. Our work provides a starting point towards the exploration of dynamical universality in higherdimensional quantum matter. 
Monday, March 14, 2022 4:48PM  5:00PM 
D50.00010: Dynamical baryon formation in $SU(n)$ Hubbard Models Miklós Antal Werner, Catalin Pascu Moca, Márton Kormos, Örs Legeza, Balázs Dóra, Gergely Zarand We study post quench dynamics in the repulsive ncolor FermiHubbard model, 
Monday, March 14, 2022 5:00PM  5:12PM 
D50.00011: Counterdiabatic Control in the Impulse Regime. Eoin Carolan, Steve Campbell, Anthony Kiely Coherent control of complex manybody systems is critical to the development of useful quantum devices. Fast perfect state transfer can be exactly achieved through additional counterdiabatic fields. We show that the additional energetic overhead associated with implementing counterdiabatic driving can be reduced while still maintaining high target state fidelities. This is achieved by implementing control fields only during the impulse regime, as identified by the KibbleZurek mechanism. We demonstrate that this strategy successfully suppresses most of the defects that would be generated due to the finite driving time for two paradigmatic settings: the LandauZener model and the Ising model. For the latter case, we also investigate the performance of our impulse control scheme when restricted to more experimentally realistic local control fields. 
Monday, March 14, 2022 5:12PM  5:24PM 
D50.00012: Freezing topological edge states after a quantum quench Justin Song, Ching Hua Lee Topological edge states are telltale signs of the nontrivial winding of wavefunctions found in topological materials. Here we argue that characteristics of such topological edge states (e.g., probability density, pseudospin density) that are prepared in a topologically nontrivial hamiltonian persist even when the hamiltonian is quenched into a trivial phase. For instance, we find that the probability density of 1D domain wall topological edge states can appear "frozen" over a long time window even after the hamiltonian is quenched into a trivial gapped phase maintaining a welldefined peaked spatial profile. After this "frozen" window, the topological boundary mode decays slowly. This behavior highlights the unusual features of nonequilibrium protocols enabling quenches to dynamically control spatially confined topological edge states in quantum quenches. 
Monday, March 14, 2022 5:24PM  5:36PM 
D50.00013: Loschmidt Amplitude Spectrum in Dynamical Quantum Phase Transitions Cheuk Yiu WONG, Wing Chi YU The theory of dynamical quantum phase transitions (DQPT) has been a paradigm in the study of manybody quantum dynamics. With the great success of theoretical descriptions supporting the experiments, the reasoning of how DQPT occur is yet to be stated. To that, we propose a scheme called "Loschmidt amplitude spectrum" to study the dynamics. Upon investigating the spectral properties of several quenches, we analytically and numerically reveal the mechanics of DQPT for both integrable and nonintegrable models. We demonstrate that the former involves a sudden population migration of momentum quasiparticles, whereas the latter alters the distribution of states having different magnetization. For the integrable model, we also show that the spectral dynamics of Loschmidt quantities behaves more violently than the groundstate quantity, where nonanalyticities can be spotted during quench within the same phase. We expect the proposed scheme is applicable to any model for indepth analysis and manages to reveal fundamental knowledge about DQPT. 
Monday, March 14, 2022 5:36PM  5:48PM 
D50.00014: Dynamics of symmetryresolved entanglement after a quench in a freefermion chain Gilles Parez Quantum entanglement and symmetries are two pillars of our understanding of quantum manybody systems. For systems with a global conserved charge, it is a nontrivial task to understand the contribution of each charge sector to the total entanglement. This socalled symmetry resolution of entanglement gained a considerable attention during the last years. In this talk, I will discuss the exact dynamics of symmetryresolved entanglement measures after a global quench in free fermonic systems. In particular, I will highlight two physical phenomena: (i) the symmetryresolved entropies start evolving after a time delay that depends on the charge sector, and (ii) there is an effective equipartition of entanglement when the charge sector is close to the mean value of the charge. We use the quasiparticle picture for the entanglement dynamics to argue that our results hold for generic integrable systems. I will conclude the talk with a series of open questions and perspectives for further developments. 
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