Quantized Superfluid Vortex Rings in the Unitary Fermi Gas

In a recent article, Yefsah \textit{et al.} [Nature \textbf{499}, 426 (2013)] report the observation of an unusual excitation in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe oscillations almost an order of magnitude slower than predicted by any theory of domain walls which they interpret as a ``heavy soliton'' of inertial mass some 200 times larger than the free fermion mass or 50 times larger than expected for a domain wall. We present compelling evidence that this ``soliton'' is instead a quantized vortex ring by showing that the main aspects of the experiment can be naturally explained within the framework of time-dependent superfluid DFT.