Dynamical Instability of a Nonequilibrium Exciton-Polariton Condensate

By imaging single-shot realizations of an organic polariton quantum fluid, we observe the long-sought dynamical instability of nonequilibrium condensates. We find an excellent agreement between the experimental data and a numerical simulation of the open-dissipative Gross-Pitaevskii equation, without performing any parameter fitting, which allows us to draw several important conclusions about the physics of the system. We find that the reservoir dynamics are in the strongly nonadiabatic regime, which renders the complex Ginzburg-Landau description invalid. The observed transition from stable to unstable fluid can only be explained by taking into account the specific form of reservoir-mediated instability as well as particle currents induced by the finite extent of the pump spot.