Reviving product states in the disordered Heisenberg chain

TL;DR

This paper demonstrates that certain product states in the disordered Heisenberg chain exhibit persistent revivals and oscillations, defying typical thermalization and challenging existing many-body localization theories.

Contribution

It introduces a class of product states with indefinite oscillations and revivals, revealing weak ergodicity breaking beyond known localized systems.

Findings

Product states show indefinite revivals and oscillations.

System neither equilibrates nor thermalizes.

Results supported by tensor network numerics up to 160 sites.

Abstract

When a generic quantum system is prepared in a simple initial condition, it typically equilibrates toward a state that can be described by a thermal ensemble. A known exception are localized systems which are non-ergodic and do not thermalize, however local observables are still believed to become stationary. Here we demonstrate that this general picture is incomplete by constructing product states which feature periodic high-fidelity revivals of the full wavefunction and local observables that oscillate indefinitely. The system neither equilibrates nor thermalizes. This is analogous to the phenomenon of weak ergodicity breaking due to many-body scars and challenges aspects of the current MBL phenomenology, such as the logarithmic growth of the entanglement entropy. To support our claim, we combine analytic arguments with large-scale tensor network numerics for the disordered Heisenberg chain. Our results hold for arbitrarily long times in chains of 160 sites up to machine precision.