We investigate single ions of Ca-40(+) in Paul traps for quantum information processing. Superpositions of the S-1/2 electronic ground state and the metastable D-5/2 state are used to implement a qubit. Laser light on the S-1/2 <----> D-5/2 transition is used for the manipulation of the ion's quantum state. We apply sideband cooling to the ion and reach the ground state of vibration with up to 99.9% probability. Starting from this Fock state = 0], we demonstrate coherent quantum state manipulation. A large number of Rabi oscillations and a ms-coherence time is observed. Motional heating is measured to be as low as one vibrational quantum in 190 ms. We also report on ground state cooling of two ions. [References: 18]
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