A single 40Ca+ ion is trapped and laser cooled to its motional ground state. Laser radiation which couples off-resonantly to a motional sideband of the ion's S1/2 to D5/2 transition causes a phase shift proportional to the ion's motional quantum state |n>. As the phase shift is conditional upon the ion's motion, we are able to demonstrate a universal 2-qubit quantum gate operation where the electronic target state {S,D} is flipped depending on the motional qubit state |n>={|0>,|1>}. Finally, we discuss scaling properties of this universal quantum gate for linear ion crystals and present numerical simulations for the generation of a maximally entangled state of five ions.
@article{arxiv.quant-ph/0307211,
title = {Quantized phase shifts and a dispersive universal quantum gate},
author = {F. Schmidt-Kaler and H. Haeffner and S. Gulde and M. Riebe and G. Lancaster and J. Eschner and C. Becher and R. Blatt},
journal= {arXiv preprint arXiv:quant-ph/0307211},
year = {2007}
}