Observation of Stark many-body localization without disorder

TL;DR

This paper experimentally demonstrates Stark many-body localization in a disorder-free quantum system, showing halted thermalization and slow correlation spread, challenging the notion that disorder is essential for MBL.

Contribution

The study provides the first direct observation of Stark MBL in a controlled quantum simulator, revealing localization without disorder and exploring its properties and implications.

Findings

Stark MBL halts thermalization in a quantum system.

Correlations propagate slowly in the localized phase.

Disorder-free regions can coexist with thermalized regions.

Abstract

Thermalization is a ubiquitous process of statistical physics, in which details of few-body observables are washed out in favor of a featureless steady state. Even in isolated quantum many-body systems, limited to reversible dynamics, thermalization typically prevails. However, in these systems, there is another possibility: many-body localization (MBL) can result in preservation of a non-thermal state. While disorder has long been considered an essential ingredient for this phenomenon, recent theoretical work has suggested that a quantum many-body system with a uniformly increasing field -- but no disorder -- can also exhibit MBL, resulting in `Stark MBL.' Here we realize Stark MBL in a trapped-ion quantum simulator and demonstrate its key properties: halting of thermalization and slow propagation of correlations. Tailoring the interactions between ionic spins in an effective field gradient, we directly observe their microscopic equilibration for a variety of initial states, and we apply single-site control to measure correlations between separate regions of the spin chain. Further, by engineering a varying gradient, we create a disorder-free system with coexisting long-lived thermalized and nonthermal regions. The results demonstrate the unexpected generality of MBL, with implications about the fundamental requirements for thermalization and with potential uses in engineering long-lived non-equilibrium quantum matter.