  We demonstrate both experimentally and theoretically that a colloidal sphere
trapped in a static optical tweezer does not come to equilibrium, but rather
reaches a steady state in which its probability flux traces out a toroidal
vortex. This non-equilibrium behavior can be ascribed to a subtle bias of
thermal fluctuations by non-conservative optical forces. The circulating sphere
therefore acts as a Brownian motor. We briefly discuss ramifications of this
effect for studies in which optical tweezers have been treated as potential
energy wells.
