Resolved-Sideband Raman Cooling to the Ground State of an Optical Lattice

We trap neutral Cs atoms in a two-dimensional optical lattice and cool them close to the zero point of motion by resolved-sideband Raman cooling. Sideband cooling occurs via transitions between the vibrational manifolds associated with a pair of magnetic sublevels, and the required Raman coupling is provided by the lattice potential itself. We obtain mean vibrational excitations ${\overline{n}}_x\approx {\overline{n}}_y<0.024\mathrm{}$, corresponding to a population $>95\mathrm{}\%$ in the vibrational ground state. Atoms in the ground state of an optical lattice provide a new system in which to explore quantum state control and subrecoil laser cooling.