Ryan Doran (Newcastle University)
From Disorder to Design: Vortex Formation, Breakup, and Interaction in Superfluids
Superfluids, such as those formed by ultra-cold atomic Bose-Einstein Condensates (BECs), have incredible properties such as the ability to flow without viscous effects and the quantization of vorticity. Although the problem of superfluid flow past a potential barrier is a well-studied problem in BECs, fewer studies have considered the case of superfluid flow through a disordered potential. I consider the case of a superfluid in a channel with multiple point-like barriers, randomly placed to form a disordered potential, and describe how the flow of the superfluid is arrested by the nucleation of vortices and the breakdown of superfluidity.
We then turn our attention to a two-component BEC in the immiscible limit. In such a system, if vortices are formed in one component, atoms in the second component will fill the vortex cores, modifying the vortex profile. We show that these vortices can be controllably nucleated, and that they support multiply quantized vortices. We also look at the case of a small bubble in the second component “stirring” the first component; here the number of vortices that are created depends on the initial size and velocity of the bubble, which can be predicted by a superfluid Weber number (a dimensionless parameter that characterizes the flow of a multiphase classical fluid).
Finally, I will mention recent work on a point vortex model for systems that support long-range dipole-dipole interactions.