Emergent thermal fluctuations and non-Hermitian phase transitions in open photon condensates

TL;DR

This paper studies the nonequilibrium behavior of open photon condensates, revealing long-lived metastable states, quasithermal fluctuations, and non-Hermitian phase transitions driven by exceptional points.

Contribution

It introduces a unified Lindblad approach to analyze condensate and fluctuations, discovering metastable states and non-Hermitian phase transitions in photon BECs.

Findings

Metastable plateau stabilized by a ghost attractor with long lifetime.

Condensate exhibits quasithermal fluctuations scaling as inverse square root of system size.

Identification of exceptional points leading to non-Hermitian phase transitions.

Abstract

We investigate the nonequilibrium dynamics of an open photon Bose-Einstein condensate in a dye-filled microcavity using a Lindblad master-equation approach, treating the condensate and the noncondensed fluctuations on the same footing. The driven-dissipative condensate exhibits a long-lived, metastable plateau stabilized by a ghost attractor, a fixed point that lies outside the physical domain in configuration space, yet stalls the condensate dynamics for exceedingly long times before it dephases to zero [Phys. Rev. Lett. 135, 053402 (2025)]. Despite the nonequilibrium origin of this dynamical stabilization, the condensate exhibits quasithermal fluctuations in the plateau in that the relative order-parameter fluctuations scale as the inverse square root of the system size. A linear stability analysis further reveals the presence of exceptional points, resulting in multiple non-Hermitian phase transitions associated with the relaxation dynamics into and out of the metastable condensate.