Emergent thermal behavior, synchronization, and non-Hermitian phase transitions in driven-dissipative photon condensates

Abstract

Driven-dissipative Bose-Einstein condensates of photons in optical resonators have been shown theoretically to exist as a long-lived, yet metastable state stabilized by a ghost attractor, despite continuous driving [Phys. Rev. Lett. 135, 053402 (2025)]. Here we analyze the properties of this metastable condensate as well as the relaxation dynamics into and out of this state by means of the Lindblad master-equation approach, treating the condensate and the equal-time, noncondensed fluctuations on the same footing. Despite its nonequilibrium origin, the quasistationary condensate exhibits thermal behavior in that the order-parameter fluctuations scale with system size as in thermodynamic equilibrium, and the photon-number distribution in multimode resonators is in excellent agreement with a Bose-Einstein distribution. A linear stability analysis further reveals the presence of several exceptional points, resulting in multiple non-Hermitian phase transitions associated with the relaxation dynamics into and out of the metastable condensate. These behaviors reconcile apparently contradictory experimental results.

arXiv comment11 pages, 10 figures. Added multimode thermalization and synchronization