  Randomly diffusing atoms confined in a dissipative optical lattice are
illuminated by a weak probe of light. The probe transmission spectrum reveals
directed atomic propagation that occurs perpendicular to the direction of probe
beam propagation. 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 simple model reveals how the probe-excited atomic density waves and
optical pumping rates conspire to create directed atomic propagation within a
randomly diffusing sample.
