Kelvin-Helmholtz Instability in annular Fermi superfluids

In this thesis I investigate the onset and evolution of the Kelvin-Helmholtz instability in fermionic superfluids across the BEC-BCS crossover. The system involves two counter-rotating annular superflows separated by a thin potential barrier. Each annular superfluid holds an opposite-sign persistent current with the same number of circulation quanta. By tuning the barrier height, we control the merging dynamics of the superfluid, and observe how the interface deforms into an ordered array of quantized vortices, which then loses stability and rolls up into vortex clusters. The Kelvin-Helmholtz instability in superfluids can be seen as the instability breaking the symmetry of the regular array of vortices. Extracting the instability growth rates from the experimental data, we find that they obey the same scaling relations across the different superfluid regimes, although vortex dynamics appears to be consistently slower than predicted.