Quench dynamics in strongly coupled laser cavities

TL;DR

This paper investigates the out-of-equilibrium dynamics of strongly coupled nanocavities, revealing transient superthermal light and mixing of thermal and coherent states, advancing understanding of far-from-equilibrium thermodynamics in optical systems.

Contribution

It demonstrates the occurrence of superthermal transient states in bimodal nanolasers after a quench and introduces a method to quantify their thermalization degree using Gibbs entropy.

Findings

Transient superthermal light observed after quench.

Detection of mixing between thermal and coherent phases.

Quantification of non-equilibrium states via Gibbs entropy.

Abstract

Strongly coupled dissipative optical cavities with nonlinear interactions give new opportunities to explore symmetry breaking phenomena and phase transitions, Josephson dynamics and quantum criticality. Among the different experimental realizations, photonic crystal coupled nanocavities operating in the laser regime are outstanding systems since nonlinearity, gain/dissipation and intercavity coupling can be judiciously tailored. Yet, although most common scenarios emerge from quasi-dynamical equilibrium where the gain nearly compensates for losses, little is known about far out-of-equilibrium dynamics resulting, for instance, from short pulsed pumping inducing a classical "quench". Here we show that bimodal nanolasers generically display transient dynamics after quench which, when projected onto the nonlasing mode, exhibit superthermal light. Such a mechanism is akin to the fast cooling of a suspension of Brownian particles under gravity, with the intracavity intensity playing the role of the inverse temperature. We implement a simple experimental technique to access the probability density functions, that enabled quantifying the distance from thermal equilibrium --and hence the degree of residual order-- via the Gibbs entropy. This allowed us to further detect mixing of thermal states with coherent broken parity phases, thus paving the road for investigating far nonequilibrium thermodynamics with multimode optical oscillators.