Dynamics of a Vortex Lattice in an Expanding Polariton Quantum Fluid

If a quantum fluid is driven with enough angular momentum, at equilibrium the ground state of system given by lattice quantised vortices whose density prescribed quantization circulation. We report on first experimental study Feynman-Onsager relation in non-equilibrium polariton fluid, free to expand and rotate. Upon initially imprinting we track vortex core positions picosecond time scales. observe an accelerated stretching outward bending linear trajectories vortices, due repulsive interactions. Access full phase fields allows us detect small deviation from rule terms transverse velocity component, gradient envelope acting lattice.