After the discovery of zero viscosity in liquid helium, other fundamental properties of the superfluidity phenomenon have been revealed. One of them, irrotational flow, gives rise to quantized vortices and persistent currents. Those are the landmarks of superfluidity in its modern understanding. Recently, a new variety of dissipationless fluid behaviour has been found in microcavities under the optical parametric regime. Here we report the observation of metastable persistent polariton superflows sustaining a quantized angular momentum, m, after applying a 2-ps laser pulse carrying a vortex state. We observe a transfer of angular momentum to the steady-state condensate, which sustains vorticity for as long as it can be tracked. Furthermore, we study the stability of quantized vortices with m=2. The experiments are analysed using a generalized two-component Gross–Pitaevskii equation. These results demonstrate the control of metastable persistent currents and show the peculiar superfluid character of non-equilibrium polariton condensates. Similar to atoms in cold gases, exciton–polaritons in semiconductor microcavities can undergo Bose–Einstein condensation, but under non-equilibrium conditions. Now, quantized vortices and persistent currents — hallmarks of superfluid behaviour — have been observed in such condensates.

Persistent currents and quantized vortices in a polariton superfluid