Long-range Ordering of Topological Excitations in a Two-Dimensional Superfluid Far From Equilibrium

Understand

We study the relaxation of a 2D ultracold Bose-gas from a nonequilibrium initial state containing vortex excitations in experimentally realizable square and rectangular traps.

• We show that the subsystem of vortex gas excitations results in the spontaneous emergence of a coherent superfluid flow with a non-zero coarse-grained vorticity field.
• The streamfunction of this emergent quasi-classical 2D flow is governed by a Boltzmann-Poisson equation.
• This equation reveals that maximum entropy states of a neutral vortex gas that describe the spectral condensation of energy can be classified into types of flow depending on whether or not the flow spontaneously acquires angular momentum.