Injection and storage of orbital angular momentum as vortices in polariton superfluids

We report the experimental investigation and theoretical modeling of a rotating polariton superfluid relying on an innovative method for the injection of angular momentum.This novel, multi-pump injection method uses four coherent lasers arranged in a square, resonantly creating four polariton populations propagating inwards. The control available over the direction of propagation of the superflows allows injecting a controllable amount of optical angular momentum. When the density at the center is low enough to neglect polariton-polariton interactions, optical singularities, associated to an interference pattern, are visible in the phase. Remarkably, in the superfluid regime resulting from the strong nonlinear polariton-polariton interaction the interference pattern disappears and only vortices with the same sign are persisting in the system. By comparing these results with simulations based on a driven-dissipative Gross-Pitaevskii model, we ascribe these remaining topological defects to the conservation of angular momentum.