Abstract

Microcavity polaritons are a system that can show coherence in a strongly-coupled light matter system at low temperatures. As such, they connect both to Bose-Einstein condensation and also to lasing, and they currently provoke a number of questions about what properties such a non-equilibrium superfluid might have. Some aspects of superfluidity, such as the observation of quantised vortices, and some experiments on scattering from defects have been studied experimentally. Theoretically, the effects of finite particle lifetime on the excitation spectrum has been discussed, and some of its consequences for superfluidity have been examined. However, the superfluid density of the non-equilibrium polariton condensate has not previously been calculated. I will present an approach to calculating superfluid density, revealing how the polariton system can show a superfluid response despite not having a linear excitation spectrum.