On the phase structure of driven quantum systems

TL;DR

This paper demonstrates that disordered, periodically driven quantum systems can exhibit various ordered phases and sharp transitions, including some with broken symmetries, topological order, and unique Floquet-specific dynamics, contrasting with the trivial phases of clean systems.

Contribution

It reveals the existence of distinct ordered phases and phase transitions in disordered Floquet many-body localized systems, expanding understanding beyond the trivial infinite-temperature phase.

Findings

Disordered Floquet systems can host ordered phases with broken symmetries.

Identification of Floquet phases with topological order.

Discovery of new Floquet-specific ordered dynamics.

Abstract

Clean and interacting periodically driven quantum systems are believed to exhibit a single, trivial "infinite-temperature" Floquet-ergodic phase. In contrast, here we show that their disordered Floquet many-body localized counterparts can exhibit distinct ordered phases delineated by sharp transitions. Some of these are analogs of equilibrium states with broken symmetries and topological order, while others - genuinely new to the Floquet problem - are characterized by order and non-trivial periodic dynamics. We illustrate these ideas in driven spin chains with Ising symmetry.