Precision AC-Stark measurement and a novel type of quantum gate

Relative AC-Stark shift of the S/sub 1/2/ and D/sub 5/2/ qubit levels in a single /sup 40/Ca/sup +/-ion is measured. A Ramsey type interferometric technique is used, where the ion is first brought into a superposition of the two qubit levels with a /spl pi//2 laser pulse, then apply the laser pulse whose influence on the relative phase evolution, and then recombine the two states with a second /spl pi//2-pulse. With this method measurement of AC-Stark shifts of less than 30 Hz in 30 s total measurement time is achieved.