By Elisabeth Giacobino, Centre National de la Recherche Scientifique
Polaritons are very special quasi-particles, which are mixtures of matter and light. In a semiconductor microcavity exciton-polaritons arise from strong coupling between cavity photons and quantum well excitons (bound electron-hole states). What makes them very attractive is the possibility of combining the coherent properties of photons with the highly interacting features of electronic states. Due to their very low mass (~10-4 times that of the electron, inherited from their photonic component), polaritons also exhibit condensation and quantum fluid properties at temperatures of a few K.
I will present our recent results, demonstrating superfluid motion of polaritons, which manifests itself as the ability to flow without friction when the flow velocity is slower than the speed of sound in the fluid. Cerenkov-like wake patterns, vortices and dark solitons are also observed when the flow velocity becomes larger than the speed of sound. If the polariton superfluid hits a large obstacle quantized vortices and dark solitons are observed. We have also shown the formation of lattices of vortex-antivortex pairs due to colliding flows of polaritons and very recently we have demonstrated the formation of ensembles of same-sign quantized vortices in an ensemble of polaritons where an orbital angular momentum is injected by the laser excitation. These properties of polaritons open the way to a new understanding of quantum fluids of light, and to promising methods for quantum simulation.