Single trapped ions interacting with low- and high-finesse optical cavities

The presence of mirrors modifies both the coherent coupling of an atom to a light mode and its spontaneous emission into the mode [1]. We study such cavity QED effects experimentally with single ions and optical cavities. We focus on two examples which are equally interesting as fundamental systems and for application in quantum information processing. (i) By retroreflecting the fluorescence of a single trapped Ba ion with a mirror 25 cm away, we observe inhibition and enhancement of the atom’s spontaneous emission. When two ions are trapped, the distant mirror creates superand subradiance. (ii) With a single trapped Ca ion we demonstrate coherent coupling of its narrow S1/2 –D5/2 “qubit” transition to amode of a high-finesse optical cavity. We also achieve deterministic coupling of the cavity standing wave to the ion’s vibrational state by controlling the ion’s position with nanometer-precision and selectively exciting vibrational state-changing transitions.