Localization to the ground state of axial motion is demonstrated for a single, trapped atom strongly coupled to the field of a high finesse optical resonator. The axial atomic motion is cooled by way of coherent Raman transitions on the red vibrational sideband. An efficient state detection scheme enabled by strong coupling in cavity QED is used to record the Raman spectrum, from which the state of atomic motion is inferred. We find that the lowest vibrational level of the axial potential with zero-point energy $\hslash {\omega }_a/2k_B=13\mu \mathrm{K}$ is occupied with probability $P_0\simeq 0.95$.

• Received 11 June 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.083602