Equilibrium and Superfluidity in Polariton Condensates*

In specially engineered light-matter structures, photons can be made to interact strongly. This leads to a wide range of collective behaviours from order-disorder phase transitions, condensation and superfluidity to topological phases. However, normally their intrinsically dissipative nature results in highly non-equilibrium conditions leading to new phenomena which have only started being explored. At the same time state-of-the-art semiconductor microcavities recently allowed us to achieve a fully thermalised polariton condensate analogous to cold atoms or liquid Helium.

I will discuss a few examples of novel non-equilibrium collective effects in polariton systems, such as the Kardar-Parisi-Zhang (KPZ) superfluid and the newly discovered rigid fluid phase, as well as the recently achieved equilibrium limit.