Nonequilibrium topological response under charge dephasing

TL;DR

This paper investigates how charge dephasing affects the topological responses of symmetry-protected topological states in open quantum systems, revealing a universal symmetry-breaking mechanism that extends beyond equilibrium conditions.

Contribution

It introduces a novel mechanism of spontaneous symmetry breaking induced by dephasing in SPT states, applicable to various symmetry types and gapless phases, highlighting a new fingerprint of topological order in open systems.

Findings

Dephasing induces strong-to-weak symmetry breaking in SPT states.

The mechanism applies to higher-form and spatially modulated symmetries.

The effect persists in gapless SPT phases.

Abstract

We explore nonequilibrium topological responses of symmetry-protected topological (SPT) states in open quantum systems subject to decoherence. For SPT wavefunctions protected by a product symmetry G $\times$ S , where G defects are decorated with S charge, we show that local dephasing of the S charge density generically induces spontaneous strong-to-weak symmetry breaking (SWSSB) of G in the resulting mixed-state ensemble. We extend this mechanism to SPT phases protected by higher-form and spatially modulated symmetries, and further to gapless SPT states, demonstrating that dephasing-induced SWSSB persists well beyond conventional gapped 0-form settings. Our results provide a qualitative, channel-defined fingerprint of SPT order that is intrinsic to open-system dynamics and goes beyond equilibrium linear response.