Spatiotemporal coherence of non-equilibrium multimode photon condensates

TL;DR

This paper investigates the spatial and temporal quantum coherence properties of photon Bose-Einstein condensates in a microcavity, revealing a transition from thermal equilibrium to multimode lasing behavior at high excitation levels.

Contribution

It provides experimental evidence of coherence behavior in photon condensates and introduces a microscopic theory explaining multimode condensation as akin to multimode lasing.

Findings

Long-range coherence above threshold

Short-range coherence below threshold

Multimode fragmentation far above threshold

Abstract

We report on the observation of quantum coherence of Bose-Einstein condensed photons in an optically-pumped, dye-filled microcavity. We find that coherence is long-range in space and time above condensation threshold, but short-range below threshold, compatible with thermal-equilibrium theory. Far above threshold, the condensate is no longer at thermal equilibrium and is fragmented over non-degenerate, spatially overlapping modes. A microscopic theory including cavity loss, molecular structure and relaxation shows that this multimode condensation is similar to multimode lasing induced by imperfect gain clamping.