Physical Review Research

Memory hierarchy for many-body localization: Emulating the thermodynamic limit

Alexander Nico-Katz, Abolfazl Bayat, Sougato Bose

Published Jul 25, 2022• 4 citations

Abstract

Local memory---the ability to extract information from a subsystem about its initial state---is a central feature of many-body localization. We introduce, investigate, and compare several information-theoretic quantifications of memory and discover a hierarchical relationship among them. We also find that while the Holevo quantity is the most complete quantifier of memory, vastly outperforming the imbalance, its decohered counterpart is significantly better at capturing the critical properties of the many-body localization transition at small system sizes. This motivates our suggestion that one can emulate the thermodynamic limit by artificially decohering otherwise quantum quantities. Applying this method to the von Neumann entropy results in critical exponents consistent with analytic predictions, a feature missing from similar small finite-size system treatments. In addition, the decohering process makes experiments significantly simpler by avoiding quantum state tomography.

DOI: 10.1103/physrevresearch.4.033070

Related papers

A Memory Hierarchy for Many-Body Localization: Emulating the Thermodynamic Limit

Alexander Nico-Katz, Abolfazl Bayat, Sougato Bose

Local memory - the ability to extract information from a subsystem about its initial state - is a central feature of many-body localization. We introduce, investigate, and compare several information-theoretic quantifications of memory and discover a hierarchical relationship among them. We also find that while the Holevo quantity is the most complete quantifier of memory, vastly outperforming the imbalance, its decohered counterpart is significantly better at capturing the critical properties of the many-body localization transition at small system sizes. This motivates our suggestion that one can emulate the thermodynamic limit by artifically decohering otherwise quantum quantities. Applying this method to the von Neumann entropy results in critical exponents consistent with analytic predictions, a feature missing from similar small finite-size system treatments. In addition, the decohering process makes experiments significantly simpler by avoiding quantum state tomography.

arXiv:2111.01146Nov 1, 20210 citations

Information-theoretic memory scaling in the many-body localization transition

Alexander Nico-Katz, Abolfazl Bayat, Sougato Bose

A key feature of many-body localization (MBL) is the breaking of ergodicity and consequently the emergence of local memory, revealed as the local preservation of information over time. As memory is necessarily a time-dependent concept, it has been partially captured by a few extant studies of dynamical quantities. However, these quantities suffer from a variety of issues which limit their value as true quantifiers of memory; thus, a fundamental and complete information-theoretic understanding of local memory in the context of MBL remains elusive. We outline these issues in detail and introduce the dynamical Holevo quantity to address them. We find that it shows clear scaling behavior across the MBL transition, and we determine a family of two-parameter scaling Ans\"atze which capture this behavior. We perform a comprehensive finite-sized scaling analysis to extract the transition point and scaling exponents.

arXiv:2009.04470Physical review. B./Physical review. BMay 25, 202212 citations

Entropy of small subsystems in thermalizing systems

Yichen Huang

We study the entropy of small subsystems in thermalizing quantum many-body systems governed by local Hamiltonians. Assuming the eigenstate thermalization hypothesis, we derive an analytical formula for the von Neumann entropy of equilibrated subsystems. This formula reveals how subsystem entropy depends on the microscopic parameters of the Hamiltonian and the macroscopic properties of the initial state. Furthermore, our results provide a theoretical explanation for recent numerical findings by Maceira and Läuchli, obtained via exact diagonalization.

arXiv:2501.18611Jan 24, 20250 citations

Work Extraction Across a Thermodynamic Hierarchy in Quantum Many-Body Systems

Akihiro Hokkyo, Masahito Ueda

Thermodynamics is operational in the sense that the very concept of thermal equilibrium depends crucially on the choice of observables, while the amount of extractable work is defined relative to the allowed operations. Here we show that isolated quantum many-body states admit a thermodynamic hierarchical structure of observables and allowed operations, where the same state can be thermal at one level of the hierarchy and athermal at another. Enlarging the set of allowed operations therefore renders such hidden athermality a potential resource for work extraction; the resulting work gain is bounded in terms of the difference between the entropy densities of the two levels. This entropy difference takes the form of the mutual-information density. We establish the bounds for three extensions of operational access: increased spatial resolution, increased duration of control, and nonlocal connectivity, which provide access to position-state Holevo information, correlations between neighboring regions and spatially nonlocal correlations, respectively. Thus the difference between entropies at different levels of the thermodynamic hierarchy governs the bound on the work gain associated with moving to a less restricted level.

quant-pharXiv:2608.31001Sep 1, 20260 citations

Is Many-Body Localization Possible in the Absence of Disorder?

Zlatko Papić, Edwin Miles Stoudenmire, Dmitry A. Abanin

Recently it has been suggested that many-body localization (MBL) can occur in translationally-invariant systems, and candidate 1D models have been proposed. We find that such models typically exhibit strong finite-size effects due to the presence of two or more vastly different energy scales, including an artificial separation of density of states into bands separated by large energy gaps. By carefully choosing the parameters of the models such that finite-size effects are minimized, we perform extensive numerical studies of small systems using exact diagonalization. Based on the variety of diagnostics, including entanglement properties and the behavior of local observables, we find the systems exhibit thermal (ergodic), rather than MBL-like behavior. Our results suggest that MBL in translationally-invariant systems with two very different energy scales is less robust than perturbative arguments suggest, possibly pointing to the importance of non-perturbative effects which induce delocalization in the thermodynamic limit.

Jan 2, 20152 citations

Disorder-Protected Suppression of Decoherence: A Falsifiable Test of Many-Body Localization as an Information Degradation Minimum

Mikheil Rusishvili

We present a mathematically controlled, sharply falsifiable framework that tests whether many-body localization (MBL) can protect quantum information against local Markovian dephasing. Using the standard phenomenology of quasi-local l-bits, a Schrieffer-Wolff transformation yields an effective classical rate equation with transition rates ~γ (J/W)² e^{-d_H/ξ}. This implies a central bound on the von Neumann entropy production: Φ ≤ C γ N (J/W)² (W ≫ J, γ ≪ J). A variational argument provides an upper bound for the Liouvillian gap. The hypothesis is subjected to a five-point falsification matrix; any single violation disproves it. We provide an open-source QuTiP implementation and numerical results for N=6, confirming the predicted scaling exponent ≈ −2 and persistent Néel imbalance. The framework is compatible with a long-lived prethermal regime and offers a concrete realization of the VES (information degradation minima) hypothesis in open many-body quantum systems. The repository contains the manuscript, executable code (QuTiP, ITensor skeleton), and all figures.

May 10, 20260 citations