Constraints induced delocalization

TL;DR

This study investigates how quenched disorder affects the dynamics of constrained quantum spin chains, finding no evidence of many-body localization due to competing effects of disorder and interactions.

Contribution

It reveals that quenched disorder acts both as on-site disorder and as interaction, preventing the onset of many-body localization in constrained systems.

Findings

No evidence of many-body localization at large disorder

Disorder acts as both on-site term and interaction

Competing effects prevent strong disorder localization

Abstract

We study the impact of quenched disorder on the dynamics of locally constrained quantum spin chains, that describe 1D arrays of Rydberg atoms in both frozen (Ising-type) and dressed (XY-type) regime. Performing large-scale numerical experiments, we observe no trace of many-body localization even at large disorder. Analyzing the role of quenched disorder terms in constrained systems we show that they act in two, distinct and competing ways: as an on-site disorder term for the basic excitations of the system, and as an interaction between excitations. The two contributions are of the same order, and as they compete (one towards localization, the other against it), one does never enter a truly strong disorder, weak interaction limit, where many-body localization occurs. Such a mechanism is further clarified in the case of XY-type constrained models: there, a term which would represent a bona-fide local quenched disorder term acting on the excitations of the clean model must be written as a series of non-local terms in the unconstrained variables. Our observations provide a simple picture to interpret the role of quenched disorder that could be immediately extended to other constrained models or quenched gauge theories.