Vortex spin in a superfluid

General relativity predicts that the curvature of spacetime induces spin rotations on a parallel transported particle. We deploy Unruh's analogue gravity picture and consider a quantised vortex embedded in a two-dimensional superfluid Bose--Einstein condensate. We show that such a vortex behaves dynamically like a charged particle with a spin in a gravitational field. The existence of a vortex spin in a superfluid complements Onsager's prediction of the quantisation of circulation, and is suggestive of potential quantum technology applications of rotating superfluids.