Quantum vortices can lose their energy as they accelerate

Quantum vortices are the most spectacular examples of topological excitations in superfluids. Their properties lie at the heart of quantum turbulence, one of the most intriguing quantum phenomena: the system that is intrinsically superfluid behaves as viscid fluid at a macroscopic scale. The answer to this question is related to a more fundamental one: do the quantum vortices move frictionlessly through the medium? Microscopic simulations, inspired by a recent experiment by Kwon et al. [Nature (London) 600, 64 (2021)], shine a new light on dissipative mechanisms of accelerated vortex motion in superfluids. Quantum vortices may lose their kinetic energy either due to the coupling to the thermal (viscid) component or due to changes of the core's structure. Within the simulations based on fully microscopic density functional theory we investigated vortex dynamics taking into account for the first time these two effects. The energy dissipation has been measured in the setup where two pairs of vortices collided and rapidly changed their direction of motion (see figure). The collision heats up the gas of quasiparticles constituting the vortex core, which evaporate and as a result part of the vortex energy is dissipated to the medium. It means that even at absolute zero temperature, vortices will dissipate energy as they move with acceleration. The same simulations show that the coupling of vortices to the thermal component dominates the experimentally measured dissipation rates.

Article details:
A. Barresi, A. Boulet, P. Magierski, G. Wlazłowski,
Dissipative dynamics of quantum vortices in fermionic superfluid,
Phys. Rev. Lett. 130, 043001 (2023) [arXiv:2207.00870].