  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.
