We demonstrate both experimentally and theoretically that a colloidal spheretrapped in a static optical tweezer does not come to equilibrium, but ratherreaches a steady state in which its probability flux traces out a toroidalvortex. This non-equilibrium behavior can be ascribed to a subtle bias ofthermal fluctuations by non-conservative optical forces. The circulating spheretherefore acts as a Brownian motor. We briefly discuss ramifications of thiseffect for studies in which optical tweezers have been treated as potentialenergy wells.
展开▼
