Observation of bistability and hysteresis in optical binding of two dielectric spheres

Using a dual-beam fiber optic trap, we have experimentally observed bistability and hysteresis in the equilibrium separations of a pair of optically bound dielectric spheres in one dimension. These observations are in agreement with our coupled system model in which the dielectric spheres modify the field propagation, and the field self-consistently determines the optical forces on the spheres. Our results reveal hitherto unsuspected complexity in the coupled light-sphere system.