Spontaneous symmetry breaking and phase coherence of a photon Bose-Einstein condensate coupled to a reservoir

TL;DR

This paper investigates the phase behavior of a photon Bose-Einstein condensate in a dye microcavity, revealing spontaneous symmetry breaking and phase coherence despite large statistical fluctuations, with implications for understanding quantum condensates.

Contribution

It demonstrates the coexistence of phase coherence and spontaneous symmetry breaking in a photon BEC under grand canonical conditions, highlighting the role of reservoir size and statistical fluctuations.

Findings

Observation of phase jumps linked to large number fluctuations

Separation of correlation timescales in the condensate

Evidence of spontaneous symmetry breaking in photon BEC

Abstract

We examine the phase evolution of a Bose-Einstein condensate of photons generated in a dye microcavity by temporal interference with a phase reference. The photo-excitable dye molecules constitute a reservoir of variable size for the condensate particles, allowing for grand canonical statistics with photon bunching, as in a lamp-type source. We directly observe phase jumps of the condensate associated with the large statistical number fluctuations and find a separation of correlation timescales. For large systems, our data reveals phase coherence and a spontaneously broken symmetry, despite the statistical fluctuations.