Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T50: ManyBody LocalizationRecordings Available

Hide Abstracts 
Sponsoring Units: DCMP Chair: Dominique Laroche, University of Florida Room: McCormick Place W474A 
Thursday, March 17, 2022 11:30AM  11:42AM 
T50.00001: Directly Obtaining Entanglement Dynamics through Quantum Correlation Transfer Functions; Demonstrating the Mechanism of ManyBody Localization Peyman Azodi, Herschel Rabitz We introduce the Quantum Correlation Transfer Function (QCTF) approach to entanglement dynamics in manybody quantum systems and employ this framework to demonstrate the mechanism of ManyBody Localization (MBL). We show that in the QCTF framework, the entanglement dynamics of the twolevel particles of a manybody quantum system can be fully characterized directly from the system's Hamiltonian, which circumvents the bottleneck of calculating the manybody system's timeevolution. This result provides a new foundation to study the Eigenstate Thermalization Hypothesis (ETH). By employing the QCTFbased approach, we demonstrate the MBL dynamics in disordered Heisenberg spin chains. Furthermore, we prove the validity of a previous fundamental conjecture regarding the MBL phase by showing that in stronglydisordered spin chains with shortrange interaction, the quantum correlation between particles is exponentially attenuated with respect to the sitetosite distance. The QCTF approach can be extended to address general issues regarding nonequilibrium quantum statistics in spin lattices with different geometries. 
Thursday, March 17, 2022 11:42AM  11:54AM 
T50.00002: Coherent pairs probe disordersuppressed quantum dynamics in a random dipolar magnet Adrian Beckert, Manuel Grimm, Nino Wili, René Tschaggelar, Gunnar Jeschke, Guy Matmon, Simon Gerber, Markus Müller, Gabriel Aeppli Quantum information processing relies on the persistent coherence of quantum states and holds great potential for application, ranging from computation to communication and metrology. However, uncontrolled interactions among quantum bits (qubits) and with their environment lead to decoherence, i.e., the loss of quantum information^{ [1,2]}. Protecting coherence is generally difficult, particularly in quantum systems with magnetic degrees of freedom which directly couple to electron spin fluctuations. Though, manybody localization (MBL) ^{[3,4]} and its precursors^{ [57]} have been predicted to suppress relaxation processes and noise in disordered magnets and, thus, to enhance coherence. 
Thursday, March 17, 2022 11:54AM  12:06PM 
T50.00003: Entanglement mean field theory and MBL in two dimensions Philip Crowley We present “entanglement mean field theory”, a statistical theory of the subsystem entanglement in eigenstates. This theory applies across the MBLthermal phase transition to a class of models with “central seed” geometry. The predictions of the theory show good agreement with numerics, even for subsystems which are intermediate to localised and thermal. 
Thursday, March 17, 2022 12:06PM  12:18PM 
T50.00004: Transient Response of Disordered Systems to an Interaction Quench Eric Dohner, Hanna Terletska, KaMing Tam, Juana Moreno, Herbert F Fotso We present a solution for the nonequilibrium dynamics of an interacting disordered system. The approach adapts the combination of the equilibrium dynamical mean field theory (DMFT) and coherent potential approximation (CPA) methods to the nonequilibrium manybody formalism using the KadanoffBaymKeldysh complex time contour. We use our time domain solution to obtain the equilibrium density of states of the disordered interacting system described by the AndersonHubbard model, bypassing the necessity for the cumbersome analytical continuation process. We further apply the nonequilibrium solution to an interaction quench of the isolated disordered system. Here, the interaction is abruptly changed from zero (noninteracting system) to another constant (finite) value at which it is subsequently kept. We observe via the timedependence of the potential, kinetic, and total energies the effect of disorder on the relaxation of the system as a function of the final interaction strength. The realtime approach has the potential to shed new light on the fundamental role of disorder in the nonequilibrium dynamics of interacting quantum systems. 
Thursday, March 17, 2022 12:18PM  12:30PM 
T50.00005: Machine learning manybody quantum phases in nonequilibrium systems with singleparticle mobility edge YiTing Hsu, Xiao Li, Colin Beveridge The manybody quantum phases in isolated quasiperiodic systems are an intriguing subject that cannot be described by the framework of equilibrium statistical mechanics. One main challenge lies in the fact that there are no wellestablished order parameters that can definitively determine the number and nature of possible dynamical phases. In particular, a nonergodic metallic phase has been proposed as a novel phase between the manybody localized and thermalized phases in the Generalized Aubry Andre model, a onedimensional quasiperiodic chain with singleparticle mobility edge (SPME). While the existence and origin of the nonergodic metal remain elusive, this phase has been conjectured as a natural consequence of the presence of SPME. In this talk, I will present a general machinelearning protocol that can determine the phase diagrams of systems with controversial phases, a situation where the conventional supervised learning is not applicable. By applying our neuralnetwork based method to study multiple different models with SPME, I will discuss the stability of the nonergodic metal and whether it originates from SPME. 
Thursday, March 17, 2022 12:30PM  12:42PM 
T50.00006: Probing localization properties of the MBL transition via an imaginary vector potential Liam C O'Brien, Gil Refael Identifying and measuring the ``localization length'' in manybody systems in the vicinity of a manybody localization transition is difficult. Following Hatano and Nelson, a recent work (Heußen, White, Refael, Phys. Rev. B 103, 064201) introduced an ``imaginary vector potential'' to a disordered ring of interacting fermions, in order to measure a localization length corresponding to the endtoend Green's function of the corresponding open chain. We employ this nonhermitian localization technique to extract the distribution of the localization length at the transition point. We find that the localizationlength distributions at the critical points are welldescribed by extreme value distributions. We explain the appearance of these distributions, as well as connect our study to the localization length identified in the avalanche model of the manybody localization transition. 
Thursday, March 17, 2022 12:42PM  12:54PM 
T50.00007: Quantum interference and disorderfree localized quantum dynamics in an interacting twodimensional lattice gauge theory Nilotpal Chakraborty, Markus Heyl, Petr Karpov, Roderich Moessner

Thursday, March 17, 2022 12:54PM  1:06PM 
T50.00008: A stabilisation mechanism for many body localisation in 2D Darryl Foo, Nyayabanta Swain, Pinaki Sengupta, Gabriel Lemarie, Shaffique Adam Experiments in cold atom systems see identical signatures of many body localisation (MBL) in both onedimensional (d=1) and twodimensional (d=2) systems despite the thermal avalanche hypothesis showing that the MBL phase is unstable for d>1. Underpinning the thermal avalanche argument is the assumption of exponential localisation of local integrals of motion (LIOMs), a result taken from the Furstenberg theorem. In this work we show that the Furstenberg theorem assumptions break down for real experimental systems, resulting in superexponential localisation of LIOMs. A more careful analysis of the quantum avalanche argument for such realistic systems shows that the critical dimension changes from d=1 to d=2, thereby bridging the divide between the experimental demonstrations of MBL in these systems and existing theoretical arguments that claim that such demonstrations are impossible. 
Thursday, March 17, 2022 1:06PM  1:18PM 
T50.00009: Theory of growth of number entropy in disordered systems Roopayan Ghosh, Marko Znidaric

Thursday, March 17, 2022 1:18PM  1:30PM 
T50.00010: Relaxation at different lengthscales in models of manybody localization Jacek Herbrych, Marcin Mierzejewski, Peter Prelovsek We study dynamical correlation functions in the randomfield Heisenberg chain, which probes the relaxation times at different length scales. Firstly, we argue that the relaxation time associated with the dynamical imbalance (examining the relaxation at the smallest length scale) decreases with disorder much faster than the one related to the dc conductivity, which probes the global response of the system. We argue that the observed dependence of relaxation on the length scale originates from local nonresonant regions (islands). The latter has particularly long relaxation times or remains frozen, allowing for nonzero dc transport via higherorder processes. Based on the numerical evidence, we introduce a toy model that suggests that the nonresonant islands' asymptotic dynamics are essential for the proper understanding of the disordered chains with manybody interactions. 
Thursday, March 17, 2022 1:30PM  1:42PM 
T50.00011: Krylov complexity in manybody localization systems ChengJu Lin, Fabian Ballar Trigueros We study the operator growth and Krylov complexity in manybody localization (MBL) systems. Using the Lanczos algorithm, the operator growth problem can be mapped to a single particle hopping problem on a semiinfinite chain with the hopping amplitudes given by the Lanczos coefficients. We find that the hopping amplitudes grow linearly along the chain with a logarithmic correction in both MBL and ergodicity phases. Moreover, in the MBL phase, the hopping amplitudes have an additional evenodd modulation and some effective randomness. We show numerical evidences which suggest that in MBL, the corresponding single particle hopping problem is localized, resulting in its bounded Krylov complexity of the operators. In addition, we obtain the spectral function and autocorrelation function in MBL from the Lanczos algorithm. By extrapolating and modeling the behavior of the Lanczos coefficients, we discuss the possible features of the spectral function in MBL in the thermodynamic limit. 
Thursday, March 17, 2022 1:42PM  1:54PM 
T50.00012: Probing manybody localization by excitedstate VQE Shuo Liu, Shixin Zhang, ChangYu Hsieh, Shengyu Zhang, Hong Yao Nonequilibrium physics including manybody localization (MBL) has attracted increasing attentions, but theoretical approaches of reliably studying nonequilibrium properties remain quite limited. We propose a systematic approach to probe MBL phases on a digital quantum computer via the excitedstate variational quantum eigensolver (VQE) and demonstrate convincing results of MBL on a quantum hardware, which we believe paves a promising way for future simulations of nonequilibrium systems beyond the reach of classical computations in the noisy intermediatescale quantum (NISQ) era. Moreover, the MBL probing protocol based on excitedstate VQE is NISQfriendly, as it can successfully differentiate the MBL phase from thermal phases with relativelyshallow quantum circuits, and it is also robust against the effect of quantum noises. 
Thursday, March 17, 2022 1:54PM  2:06PM 
T50.00013: MBLErgodic Transitions in Systems with Correlated Disorder Rajdeep Sensarma, Abhisek Samanta, AHANA CHAKRABORTY We study transitions from many body localized to ergodic phase in one dimensional spin systems with correlated disorder. Using two different parameters to tune the width and correlations of the random couplings separately, we derive a phase diagram in the widthcorrelation plane. We understand the phase diagram in terms of an effective single parameter related to the sample variance of the couplings. This allows us to track the phase boundary analytically in this model. 
Thursday, March 17, 2022 2:06PM  2:18PM 
T50.00014: Localization in twodimensional manybody quasiperiodic models Claudio Castelnovo, Antonio Strkalj, Elmer V Doggen Manybody localization (MBL) provides a mechanism to avoid thermalization in interacting systems. It is well understood that the MBL phase can exist in closed onedimensional systems subjected to random disorder, quasiperiodic modulations, or homogeneous electric fields. However, the fate of MBL in higher dimensions remains unclear. Although some experiments on randomly disordered twodimensional (2D) systems observe a stable MBL phase on intermediate time scales, recent theoretical works show that the phenomenon cannot persist forever and in a thermodynamic limit due to the rare regions and the avalanche instability. On the other hand, quasiperiodic systems do not host rare regions, and the avalanche instability is avoided; yet, the existence of an MBL phase in these systems remains to date largely unexplored. Using the numerical method of timedependent variational principle, we investigate the localization properties of the manybody 2D AubryAndre´ quasiperiodic model by studying its outofequilibrium dynamics. We show that a stable MBL phase exists in the thermodynamic limit, in contrast to random disorder. Furthermore, we show that deterministic lines of weak potential, which appear in this model, support transport while keeping the localized parts of the system unchanged. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700