Quantum turbulence in a fluid of light.

Turbulent phenomena are among the most striking effects that both classical and quantum fluids can exhibit. While classical turbulence is ubiquitous in nature, the observation of quantum turbulence requires the precise manipulation of quantum fluids such as superfluid helium or atomic Bose-Einstein condensates. Here we discuss our recent experimental results showing the turbulent dynamics of a two-dimensional quantum fluid of exciton-polaritons, hybrid light-matter quasiparticles that arise from the strong light-matter coupling in semiconductor microcavities. By measuring the kinetic energy spectrum and the onset of vortex clustering, we demonstrate the tendency of the vortex-gas towards highly excited configurations despite the dissipative nature of the system. In particular, we discuss the inverse energy cascade and its first direct measurement in a two-dimensional quantum fluid. We highlight the advantages of optical systems in the analysis of turbulent flows and the differences with respect to Bose-Einstein condensates of ultracold atoms. These results lay the basis for the investigations of quantum turbulence in two-dimensional fluids of light.