Josephson vortices induced by phase twisting a polariton superfluid

Quantum fluids of light are an emerging platform for energy-efficient signal processing, ultrasensitive interferometry and quantum simulators at elevated temperatures. Here we demonstrate all-optical control of the topological excitations in a large polariton condensate realizing the bosonic analogue of a long Josephson junction and inducing the nucleation of Josephson vortices. When a phase difference is imposed at the boundaries of the condensate, two extended regions become separated by a sharp phase jump of pi radians and a solitonic depletion of the density, forming an insulating barrier with a suppressed order parameter. The superfluid behaviour-characterized by a smooth phase gradient across the system instead of the sharp phase jump-is recovered at higher polariton densities and is mediated by the nucleation of Josephson vortices within the barrier. Our results contribute to the understanding of dissipation and stability of elementary excitations in macroscale quantum systems.