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

Relative AC-Stark shift of the S₁2/ and D₅2/ qubit levels in a single ⁴⁰Ca⁺-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 π/2 laser pulse, then apply the laser pulse whose influence on the relative phase evolution, and then recombine the two states with a second π/2-pulse. With this method measurement of AC-Stark shifts of less than 30 Hz in 30 s total measurement time is achieved.