Constraint-Induced Delocalization

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 the 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 nonlocal 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.

Automated summary

In this study, the impact of quenched disorder on the dynamics of locally constrained quantum spin chains was investigated. Large-scale numerical experiments revealed no evidence of many-body localization even under high disorder. The analysis showed that quenched disorder terms in constrained systems act in two distinct and competing ways, preventing the system from entering into a regime of strong disorder and weak interaction where many-body localization occurs. Through observations in XY-type constrained models, it was further clarified that local quenched disorder terms must be represented as a series of nonlocal terms in unconstrained variables.