Uncovering the non-equilibrium phase structure of an open quantum spin system

TL;DR

This study explores the non-equilibrium phase structure of a driven-dissipative quantum spin system, revealing power-law scaling in population loss and identifying various regimes, thus advancing understanding of quantum systems out of equilibrium.

Contribution

It experimentally and theoretically uncovers the non-equilibrium phase structure of a controlled quantum spin system, highlighting the role of population loss rate as a key observable.

Findings

Population loss rate exhibits power-law scaling with driving strength.

Identifies dissipation-dominated, paramagnetic, and critical regimes.

Discovers an instability leading to high excitation density states.

Abstract

We experimentally and theoretically investigate the non-equilibrium phase structure of a well-controlled driven-disspative quantum spin system governed by the interplay of coherent driving, spontaneous decay and long-range spin-spin interactions. We discover that the rate of population loss provides a convenient macroscopic observable that exhibits power-law scaling with the driving strength over several orders of magnitude. The measured scaling exponents reflect the underlying non-equilibrium phase structure of the many-body system, which includes dissipation-dominated, paramagnetic and critical regimes as well as an instability which drives the system towards states with high excitation density. This opens up a new means to study and classify quantum systems out of equilibrium and extends the domain where scale-invariant behavior may be found in nature.