Sympathetic ground-state cooling and coherent manipulation with two-ion crystals

We have cooled a two-ion crystal to the ground-state of its collective mode s of motion. Laser cooling, more specifically resolved sideband cooling, is performed sympathetically by illuminating only one of the two Ca-40(+) ion s in the crystal. The heating rates of the motional modes of the crystal in our linear trap have been measured, and we found them considerably smaller than those previously reported by Turchette et al (2000 Phys.Rev.A 61 0634 18) in the case of trapped Be-9(+) ions. After the ground state is prepared , coherent quantum state manipulation of the atomic population can be perfo rmed. Up to 12 Rabi oscillations are observed, showing that many coherent m anipulations can be achieved. Coherent excitation of each ion individually and ground state cooling are important tools for the realization of quantum information processing in ion traps.