Dynamics of single-atom motion observed in a high-finesse cavity

We investigate mechanical forces on single atoms in a high-finesse optical cavity containing less than one photon on average. We count the number of a toms strongly coupled to the cavity mode close to an antinode and measure t he intensity autocorrelation function of the pump light transmitted through the cavity. Distinct features are observed and attributed to the dipole fo rce, diffusion, and velocity-dependent force, as predicted by the work of H orak et al. Our data agree well with the results of a Monte Carlo simulatio n.