Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2602.19586 · Physical review. B./Physical review. B

From Quantum Chaos to a Reversed Quantum Disentangled Liquid in a Disorder-Free Spin Ladder

Hanieh Najafzadeh, Abdollah Langari

cond-mat.str-elcond-mat.stat-mechquant-phSubmitted Feb 23, 2026• Announced Feb 24, 2026• 0 citations
v1 · Feb 23, 2026v2 · Apr 16, 2026
arXivHTMLPDF

Abstract

The mechanisms by which isolated interacting quantum systems evade thermalization extend beyond disorder-induced many-body localization, encompassing a growing class of interaction-driven phenomena. We investigate a spin-1/2 ladder with asymmetric XY leg couplings and tunable Ising interactions on the rungs, and identify the microscopic origin of many-body localization (MBL) in this setting. Through a suite of diagnostics -including entanglement dynamics, fidelity susceptibility, adiabatic gauge potential norms, level-spacing statistics and entropy of eigenstates- we uncover a reentrant progression of dynamical regimes as the rung coupling Jz is varied: integrable behavior at Jz=0, quantum chaos at intermediate Jz, and a robust nonthermal regime at strong coupling. In the latter regime, we demonstrate the emergence of a reversed quantum disentangled liquid (reversed-QDL), where the light species thermalizes while the heavy species remains localized. The strong-coupling limit further yields emergent local integrals of motion anchored in a fixed-point structure, providing a microscopic origin of the observed quasi-MBL dynamics. These results establish reversed-QDL as a distinct, disorder-free route to nonergodicity and broaden the classification of dynamical phases in quantum matter.

Journal reference
Phys. Rev. B. 113, 144308 (2026)
DOI
10.1103/12pf-d8p8

Related papers

Partial breakdown of quantum thermalization in a Hubbard-like model

James R. Garrison, Ryan V. Mishmash, Matthew P. A. Fisher

In recent years, physicists have made great strides toward better understanding isolated many-body quantum systems. Already, two distinct phases are well known: systems that are ergodic and thermalize completely, and, by contrast, systems that exhibit many-body localization (MBL) due to a strong disorder potential, which prevents thermalization. It is tempting to wonder whether a phase of matter could exist between the extremes of full thermalization and MBL in a generic, i.e., nonintegrable, isolated many-body quantum system. Here, the authors provide evidence that such a nonergodic phase can be realized in a translationally invariant itinerant electron model, with both charge and spin degrees of freedom. Exact diagonalization calculations on finite system sizes reveal that there exists a ``spin band'' of nonthermal eigenstates. These states have entanglement entropy that scales as an overall ``volume law,'' but after a partial measurement of the spin on each site the scaling is modified to an ``area law,'' thus suggesting the states are not ergodic. These properties and others suggest that this model realizes a new nonthermal phase of matter, known as a quantum disentangled liquid (QDL). The putative existence of this phase has striking implications for the foundations of quantum statistical mechanics.

arXiv:1606.05650•Physical review. B./Physical review. B•Feb 17, 2017•28 citations

Exploration of the existence of a distinct quasi many-body localized phase: Numerical study of a translationally invariant system in the thermodynamic limit

Jesko Sirker

We consider a quench in an infinite spin ladder describing a system with two species of bosons in the limit of strong interactions. If the heavy bosonic species has infinite mass, the model becomes a spin chain with quenched binary disorder which shows true Anderson localization (AL) or many-body localization (MBL). For finite hopping amplitude ${J}^{\ensuremath{'}}$ of the heavy particles, on the other hand, we find an exponential polarization decay with a relaxation rate which depends monotonically on ${J}^{\ensuremath{'}}$. Furthermore, the entanglement entropy changes from a constant (AL) or logarithmic (MBL) scaling in time $t$ for ${J}^{\ensuremath{'}}=0$ to a subballistic power law, ${S}_{\mathrm{ent}}\ensuremath{\sim}{t}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}<1$, for finite ${J}^{\ensuremath{'}}$. We do not find a distinct regime in time where the dynamics for ${J}^{\ensuremath{'}}\ensuremath{\ne}0$ shows the characteristics of an MBL phase. Instead, we discover a time regime with distinct dephasing and entanglement times, leading to dynamics in this regime which is different both from a localized and from a fully ergodic phase.

arXiv:1805.08258•Physical review. B./Physical review. B•Feb 28, 2019•14 citations

Phenomenology of Many-Body Localization in Bond-Disordered Spin Chains

Adith Sai Aramthottil, Piotr Sierant, Maciej Lewenstein +1 more

Many-body localization (MBL) hinders the thermalization of quantum many-body systems in the presence of strong disorder. In this Letter, we study the MBL regime in bond-disordered spin-1/2 XXZ spin chain, finding the multimodal distribution of entanglement entropy in eigenstates, sub-Poissonian level statistics, and revealing a relation between operators and initial states required for examining the breakdown of thermalization in the time evolution of the system. We employ a real space renormalization group scheme to identify these phenomenological features of the MBL regime that extend beyond the standard picture of local integrals of motion relevant for systems with disorder coupled to on-site operators. Our results pave the way for experimental probing of MBL in bond-disordered spin chains.

arXiv:2405.10062•Physical Review Letters•Nov 8, 2024•7 citations

Stability and quasi-periodicity of many-body localized dynamics

Peyman Azodi, HERSCHEL A. RABITZ

Abstract The connection between entanglement dynamics and non-equilibrium statistics in isolated many-body quantum systems has been established both theoretically and experimentally. Many-body localization (MBL), a phenomenon where interacting particles in disordered (i.e. random) chains fail to thermalize, exemplifies this connection. However, the systematic proof of critical phenomena such as MBL remains challenging due to the lack of robust methods for analyzing many-body entanglement dynamics. In this paper, we identify MBL through quasi-periodic dynamics in the entanglement evolution of subsystems in a disordered Heisenberg chain. This new form of characterizing MBL, through stable quasi-periodic dynamics of entanglement-where ‘stable’ means they persist in the thermodynamic limit—concretely distinguishes between two competing scenarios: fully localized behavior of subsystems or slowly, exponentially slow in disorder, thermalizing subsystems—a heated controversy in the literature. Utilizing perturbation theory, we derive the entanglement dynamics of single spins through an infinite perturbative series, while also modeling rare Griffiths regions (locally thermal inclusions). Our results prove that in regimes of sufficiently strong disorder, the entanglement evolution of individual subsystems remains quasi-periodic in the thermodynamic limit, thereby providing concrete evidence for the stability of MBL dynamics in disordered Heisenberg chains. This behavior contrasts with the widely reported logarithmic growth of subsystem entanglement in the MBL phase. We show that the logarithmic growth observed in prior studies arises from statistical ensemble averaging, which is prohibited due to the intrinsic non-ergodic dynamics characteristic of MBL systems, rooted in their quasi-periodic features.

arXiv:2201.11223•New Journal of Physics•Jul 1, 2025•1 citation

Quantum disentangled liquid in the half-filled Hubbard model

Thomas Veness, Fabian H. L. Eßler, Matthew P. A. Fisher

Our expectation of thermalization is one borne of experience, and it is interesting to understand how conventional statistical mechanics may fail. The so-called quantum disentangled liquid (QDL) is a paradigm outside of the (Generalized) Gibbs description, but also without spatial disorder, precluding many-body localization. In this paper, the authors provide evidence that this QDL behavior exists in the Hubbard model. The QDL diagnostic involves bipartite entanglement entropies after a partial measurement. Both integrability in 1D and strong-coupling techniques are used to argue that the QDL diagnostic is indeed satisfied.

arXiv:1611.02075•Physical review. B./Physical review. B•Nov 27, 2017•22 citations

Adiabatic Ramp Dynamics Across the ETH--MBL Transition in Disordered XXZ Spin Chain

Nidhi Kumari, Vinod Ashokan

Many-body localization(MBL) provides a mechanism by which isolated interacting quantum systems with disorder can avoid thermalization unlike ergodic systems satisfying the eigenstate thermalization hypothesis(ETH). Many-body localized systems retain signatures of their initial conditions at long times, whereas systems obeying ETH lose such information as they approach thermal equilibrium. Studying Non-equilibrium dynamics across ETH-MBL crossover is an important problem in condensed matter physics. Adiabatic control of parameters in interacting disordered systems provides a powerful framework to investigate MBL phases and their dynamical robustness. Using exact diagonalization and time-dependent numerical methods we study the effects of adiabatically ramped interactions in a disordered spin-1/2 XXZ chain, a paradigmatic model for exploring the many-body localization transition. By monitoring diagonal entropy density and entanglement entropy density growth across various ramp speeds, and system sizes. Our study incorporates Finite-size effects of spectral observables to probe the transition between ergodic and localized phases. The numerical results show that localized dynamical behavior remains largely intact under sufficiently slow ramp evolution, while increasing the driving rate promotes stronger excitation generation and larger entropy growth. This trend highlights the strong dependence of nonequilibrium adiabatic dynamics in disordered interacting quantum many-body systems.

arXiv:2606.04926•Jun 3, 2026•0 citations
The mechanisms by which isolated interacting quantum systems evade thermalization extend beyond disorder-induced many-body localization, encompassing a growing class of interaction-driven phenomena. We investigate a spin-1/2 ladder with asymmetric XY leg couplings and tunable Ising interactions on the rungs, and identify the microscopic origin of many-body localization (MBL) in this setting. Through a suite of diagnostics -including entanglement dynamics, fidelity susceptibility, adiabatic gauge potential norms, level-spacing statistics and entropy of eigenstates- we uncover a reentrant progression of dynamical regimes as the rung coupling Jz is varied: integrable behavior at Jz=0, quantum chaos at intermediate Jz, and a robust nonthermal regime at strong coupling. In the latter regime, we demonstrate the emergence of a reversed quantum disentangled liquid (reversed-QDL), where the light species thermalizes while the heavy species remains localized. The strong-coupling limit further yields emergent local integrals of motion anchored in a fixed-point structure, providing a microscopic origin of the observed quasi-MBL dynamics. These results establish reversed-QDL as a distinct, disorder-free route to nonergodicity and broaden the classification of dynamical phases in quantum matter.
In recent years, physicists have made great strides toward better understanding isolated many-body quantum systems. Already, two distinct phases are well known: systems that are ergodic and thermalize completely, and, by contrast, systems that exhibit many-body localization (MBL) due to a strong disorder potential, which prevents thermalization. It is tempting to wonder whether a phase of matter could exist between the extremes of full thermalization and MBL in a generic, i.e., nonintegrable, isolated many-body quantum system. Here, the authors provide evidence that such a nonergodic phase can be realized in a translationally invariant itinerant electron model, with both charge and spin degrees of freedom. Exact diagonalization calculations on finite system sizes reveal that there exists a ``spin band'' of nonthermal eigenstates. These states have entanglement entropy that scales as an overall ``volume law,'' but after a partial measurement of the spin on each site the scaling is modified to an ``area law,'' thus suggesting the states are not ergodic. These properties and others suggest that this model realizes a new nonthermal phase of matter, known as a quantum disentangled liquid (QDL). The putative existence of this phase has striking implications for the foundations of quantum statistical mechanics.
We consider a quench in an infinite spin ladder describing a system with two species of bosons in the limit of strong interactions. If the heavy bosonic species has infinite mass, the model becomes a spin chain with quenched binary disorder which shows true Anderson localization (AL) or many-body localization (MBL). For finite hopping amplitude ${J}^{\ensuremath{'}}$ of the heavy particles, on the other hand, we find an exponential polarization decay with a relaxation rate which depends monotonically on ${J}^{\ensuremath{'}}$. Furthermore, the entanglement entropy changes from a constant (AL) or logarithmic (MBL) scaling in time ttt for ${J}^{\ensuremath{'}}=0$ to a subballistic power law, ${S}_{\mathrm{ent}}\ensuremath{\sim}{t}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}<1$, for finite ${J}^{\ensuremath{'}}$. We do not find a distinct regime in time where the dynamics for ${J}^{\ensuremath{'}}\ensuremath{\ne}0$ shows the characteristics of an MBL phase. Instead, we discover a time regime with distinct dephasing and entanglement times, leading to dynamics in this regime which is different both from a localized and from a fully ergodic phase.
Many-body localization (MBL) hinders the thermalization of quantum many-body systems in the presence of strong disorder. In this Letter, we study the MBL regime in bond-disordered spin-1/2 XXZ spin chain, finding the multimodal distribution of entanglement entropy in eigenstates, sub-Poissonian level statistics, and revealing a relation between operators and initial states required for examining the breakdown of thermalization in the time evolution of the system. We employ a real space renormalization group scheme to identify these phenomenological features of the MBL regime that extend beyond the standard picture of local integrals of motion relevant for systems with disorder coupled to on-site operators. Our results pave the way for experimental probing of MBL in bond-disordered spin chains.
Abstract The connection between entanglement dynamics and non-equilibrium statistics in isolated many-body quantum systems has been established both theoretically and experimentally. Many-body localization (MBL), a phenomenon where interacting particles in disordered (i.e. random) chains fail to thermalize, exemplifies this connection. However, the systematic proof of critical phenomena such as MBL remains challenging due to the lack of robust methods for analyzing many-body entanglement dynamics. In this paper, we identify MBL through quasi-periodic dynamics in the entanglement evolution of subsystems in a disordered Heisenberg chain. This new form of characterizing MBL, through stable quasi-periodic dynamics of entanglement-where ‘stable’ means they persist in the thermodynamic limit—concretely distinguishes between two competing scenarios: fully localized behavior of subsystems or slowly, exponentially slow in disorder, thermalizing subsystems—a heated controversy in the literature. Utilizing perturbation theory, we derive the entanglement dynamics of single spins through an infinite perturbative series, while also modeling rare Griffiths regions (locally thermal inclusions). Our results prove that in regimes of sufficiently strong disorder, the entanglement evolution of individual subsystems remains quasi-periodic in the thermodynamic limit, thereby providing concrete evidence for the stability of MBL dynamics in disordered Heisenberg chains. This behavior contrasts with the widely reported logarithmic growth of subsystem entanglement in the MBL phase. We show that the logarithmic growth observed in prior studies arises from statistical ensemble averaging, which is prohibited due to the intrinsic non-ergodic dynamics characteristic of MBL systems, rooted in their quasi-periodic features.
Our expectation of thermalization is one borne of experience, and it is interesting to understand how conventional statistical mechanics may fail. The so-called quantum disentangled liquid (QDL) is a paradigm outside of the (Generalized) Gibbs description, but also without spatial disorder, precluding many-body localization. In this paper, the authors provide evidence that this QDL behavior exists in the Hubbard model. The QDL diagnostic involves bipartite entanglement entropies after a partial measurement. Both integrability in 1D and strong-coupling techniques are used to argue that the QDL diagnostic is indeed satisfied.
Many-body localization(MBL) provides a mechanism by which isolated interacting quantum systems with disorder can avoid thermalization unlike ergodic systems satisfying the eigenstate thermalization hypothesis(ETH). Many-body localized systems retain signatures of their initial conditions at long times, whereas systems obeying ETH lose such information as they approach thermal equilibrium. Studying Non-equilibrium dynamics across ETH-MBL crossover is an important problem in condensed matter physics. Adiabatic control of parameters in interacting disordered systems provides a powerful framework to investigate MBL phases and their dynamical robustness. Using exact diagonalization and time-dependent numerical methods we study the effects of adiabatically ramped interactions in a disordered spin-1/2 XXZ chain, a paradigmatic model for exploring the many-body localization transition. By monitoring diagonal entropy density and entanglement entropy density growth across various ramp speeds, and system sizes. Our study incorporates Finite-size effects of spectral observables to probe the transition between ergodic and localized phases. The numerical results show that localized dynamical behavior remains largely intact under sufficiently slow ramp evolution, while increasing the driving rate promotes stronger excitation generation and larger entropy growth. This trend highlights the strong dependence of nonequilibrium adiabatic dynamics in disordered interacting quantum many-body systems.