Observation of stochastic resonance in directed propagation of cold atoms

A weak probe of light illuminates randomly diffusing atoms confined in a dissipative optical lattice. The probe transmission spectrum reveals directed propagation of a specific velocity-class of atoms. Resonant enhancement of this directed propagation is observed as we vary the random photon scattering rate. We experimentally characterize this stochastic resonance as a function of probe intensity and lattice well depth. A novel one-dimensional model reveals how the probe-excited atomic density waves and optical pumping rates conspire to create directed atomic propagation within a randomly diffusing sample.