Real-time observation of fluctuations at the driven-dissipative Dicke phase transition

TL;DR

This paper experimentally investigates how dissipation affects the driven Dicke quantum phase transition in a Bose-Einstein condensate coupled to an optical cavity, revealing real-time density fluctuations and divergence near the transition.

Contribution

It provides the first real-time observation of fluctuations at the driven-dissipative Dicke phase transition, incorporating dissipation effects into the analysis.

Findings

Density fluctuations diverge near the phase transition

Dissipation causes deviations from closed-system behavior

Extracted damping rates match theoretical models

Abstract

We experimentally study the influence of dissipation on the driven Dicke quantum phase transition, realized by coupling external degrees of freedom of a Bose-Einstein condensate to the light field of a high-finesse optical cavity. The cavity provides a natural dissipation channel, which gives rise to vacuum-induced fluctuations and allows us to observe density fluctuations of the gas in real-time. We monitor the divergence of these fluctuations over two orders of magnitude while approaching the phase transition and observe a behavior which significantly deviates from that expected for a closed system. A correlation analysis of the fluctuations reveals the diverging time scale of the atomic dynamics and allows us to extract a damping rate for the external degree of freedom of the atoms. We find good agreement with our theoretical model including both dissipation via the cavity field and via the atomic field. Utilizing a dissipation channel to non-destructively gain information about a quantum many-body system provides a unique path to study the physics of driven-dissipative systems.