Propagating wave packets and quantized currents in coherently driven polariton superfluids.

We study the properties of propagating polariton wave packets and their connection to the stability of doubly charged vortices. Wave-packet propagation and related photoluminescence spectra exhibit a rich behavior dependent on the excitation regime. We show that, because of the nonquadratic polariton dispersion, doubly charged vortices are stable only when initiated in wave packets propagating at small velocities. Vortices propagating at larger velocities, or those imprinted directly into the polariton optical parametric oscillator signal and idler, are unstable to splitting.