Thermodynamic Irreversibility in Optical Bistability

We demonstrate thermodynamic irreversibility in the stochastic switching of a coherently driven bistable optical cavity. We present measurements of phase space probability currents evidencing the breaking of detailed balance associated with thermodynamic irreversibility. We also estimate the magnitude of the irreversibility via the relative entropy of up and down switches. Our experimental observations are supported by a theoretical model, illustrating how the magnitude of the irreversibility of composite systems strongly depends on the interactions between subsystems (modes) regardless of their driven-dissipative nature. Our work establishes driven-dissipative optical resonators as a platform for experiments in stochastic thermodynamics, which could in turn help answer the long-standing question of what is the minimum energy required for an optical switch.