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 atoms strongly coupled to the cavity mode close to an antinode and measure the intensity autocorrelation function of the pump light transmitted through the cavity. Distinct features are observed and attributed to the dipole force, diffusion, and velocity-dependent force, as predicted by the work of Horak et al. Our data agree well with the results of a Monte Carlo simulation.