arXiv2020
The existence of quantized vortices is a key feature of Bose-Einstein condensates. In equilibrium condensates only quantum vortices of unit topological charge are stable, due to the dynamical instabilities of multiply charged defects, unless supported by strong external rotation. Due to immense fundamental interest in the physics of these fundamental topological excitations, a great deal of work has been expended towards understanding ways to force their stability. Here we show that in photonic Bose-Einstein condensates of exciton-polariton quasiparticles pumped in an annular geometry, not only do the constant particle fluxes intrinsic to the system naturally stabilize multiply charged vortex states, but that such states can indeed form spontaneously during the condensate formation through a dynamical symmetry breaking mechanism. We elucidate the properties of these novel states, notably finding that they radiate acoustically, in a process analogous to the emission of gravitational waves from binary black holes. Finally, we show that the vorticity of these photonic fluids are fundamentally limited by a quantum Kelvin-Helmholtz instability, and therefore by the condensate radius and pumping intensity. This represents the first report of this instability - deeply fundamental in fluid dynamics - in a quantum photonic fluid.