Finite temperature Dicke phase transition of a Bose-Einstein condensate in an optical cavity

TL;DR

This paper develops a finite temperature theory for the Dicke phase transition in a Bose-Einstein condensate within an optical cavity, explaining experimental observations and predicting new phase coexistence phenomena.

Contribution

It introduces a finite temperature model including atom-photon nonlinear interactions, extending the original Dicke model to better match experimental conditions.

Findings

Experimental phase transition explained by the model

Discovery of a coexistence phase of normal and superradiant states

Specific heat as a probe for different phases

Abstract

Dicke model predicts a quantum phase transition from normal to superradiant phases for a two-level atomic ensemble coupled with an optical cavity at zero temperature. In a recent pioneer experiment [Nature 464, 1301 (2010)], such a phase transition has been observed using a Bose-Einstein condensate (BEC) in an optical cavity. Compared with the original Dicke model, the experimental system features finite temperature and strong atom-photon nonlinear interaction in BEC. In this Letter, we develop a finite temperature theory for the Dicke phase transition of a BEC in an optical cavity, taking into account the atom-photon nonlinear interaction. In addition to explaining the experimentally observed transition from normal to superradiant phases at finite-temperature, we point it out that a new phase, the coexistence of normal and superradient phases, was also observed in the experiment. We show rich finite temperature phase diagrams existing in the experimental system by tuning various experimental parameters. We find that the specific heat of the BEC can serve as a powerful tool for probing various phases.