Anomalous collective dynamics in optically driven colloidal rings

Three fluid-borne colloidal spheres circulating around a ringlike optical vortex trap have been predicted to undergo periodic collective motion due to their hydrodynamic coupling. In fact, the quenched disorder in an experimentally projected optical vortex drives a transition to a dynamical state characterized by power-law divergence of phase-space trajectories and collective fluctuations characterized by noninteger exponents. The observed relationship between scaling in the microscopic trajectories and macroscopic collective fluctuations is consistent with predictions for the onset of weak chaos within the experimentally accessible time window.