  A single colloidal sphere circulating around a periodically modulated optical
vortex trap can enter a dynamical state in which it intermittently alternates
between freely running around the ring-like optical vortex and becoming trapped
in local potential energy minima. Velocity fluctuations in this randomly
switching state still are characterized by a linear Einstein-like diffusion
law, but with an effective diffusion coefficient that is enhanced by more than
two orders of magnitude.
