Observation of stochastic resonance in an optical lattice: Interplay of probe-modified potentials and optical pumping rates

We illuminate cold atoms diffusing around inside a dissipative optical lattice with a weak probe beam and detect the probe transmission spectrum. We find that the probe induces directed propagation of the atoms in a direction perpendicular to the probe propagation, even for probe intensities lower than 1% of the lattice intensity. We observe a resonant enhancement in the directed propagation of the cold atoms as we vary the photon scattering rate. This resonant response of the system (i.e., the atom) as a function of random environmental noise (i.e., photon scattering) is a signature of stochastic resonance. We present a simple one-dimensional model that reveals how the probe-modified ground state lattice potentials and optical pumping rates conspire to produce resonant directed propagation. We also experimentally characterize the stochastic resonance as a function of system parameters such as modulation amplitude and lattice well-depth.