Universal dynamics in the expansion of vortex clusters in a dissipative two-dimensional superfluid*

A large ensemble of quantum vortices in a superfluid may itself be treated as a novel kind of fluid that exhibits anomalous hydrodynamics [1]. In this talk, I’ll consider the dynamics of vortex clusters under thermal friction and present an analytic solution that uncovers a new universality class in the out-of-equilibrium dynamics of dissipative superfluids. The long-time dynamics of the vorticity distribution is universal in the form of an expanding Rankine vortex (i.e., top-hat distribution) independent of initial conditions. This highlights a fundamentally different decay process to classical fluids, where the Rankine vortex is forbidden by viscous diffusion. Experimental results of expanding vortex clusters in a quasi-two-dimensional Bose-Einstein condensate are in excellent agreement with the vortex fluid theory predictions. Our theoretical, numerical, and experimental results establish the validity of the vortex fluid theory for superfluid systems [2].

[1] X. Yu and A. S. Bradley, Phys. Rev. Lett. 119, 185301 (2017).
[2] O. R. Stockdale et. al., Phys. Rev. Res. 2, 033138 (2020).