Precision measurement and compensation of optical Stark shifts for an   ion-trap quantum processor
  Using optical Ramsey interferometry, we precisely measure the laser-induced AC-stark shift on the $S_{1/2}$ -- $D_{5/2}$ "quantum bit" transition near 729 nm in a single trapped $^{40}$Ca$^+$ ion. We cancel this shift using an additional laser field. This technique is of particular importance for the implementation of quantum information processing with cold trapped ions. As a simple application we measure the atomic phase evolution during a $n \times 2\pi$ rotation of the quantum bit. 
H. Haeffner, S. Gulde, M. Riebe, G. Lancaster, C. Becher, J. Eschner,   F. Schmidt-Kaler, and R. Blatt