Rodney E. S. Polkinghorne

arXiv2021

Two Nambu-Goldstone zero modes for rotating Bose-Einstein condensates

We consider rotating finite size vortex arrays in Bose-Einstein condensates that are confined by cylindrically symmetric external potentials. We show that such systems possess two exact Nambu-Goldstone zero modes associated with two spontaneously broken continuous symmetries of the system. We verify our analytical result via direct numerical diagonalizations of the Bogoliubov-de Gennes equations. We conclude by comparing rotating vortex lattices in superfluids to supersolids and discrete time crystals.

cond-mat.quant-gas↗

arXiv2021

Geometric phases of a vortex in a superfluid

We consider geometric phases of mobile quantum vortices in superfluid Bose-Einstein condensates. Haldane and Wu [Phys. Rev. Lett. 55, 2887 (1985)] showed that the geometric phase, $γ_{\mathcal C}=2πN_{\mathcal C}$, of such a vortex is determined by the number of condensate atoms $N_{\mathcal C}$ enclosed by the vortex trajectory. Considering an experimentally realistic freely orbiting vortex leads to an apparent disagreement with this prediction. We resolve it using the superfluid electrodynamics picture, which allows us to identify two additional contributions to the measured geometric phase; (i) a topologically protected edge current of vortices at the condensate boundary, and (ii) a superfluid displacement current. Our results generalise to, and pave the way for experimental measurements of vortex geometric phases using scalar and spinor Bose--Einstein condensates, and superfluid Fermi gases.

cond-mat.quant-gas↗