Quantized AC-Stark shifts and their use for multiparticle entanglement and quantum gates
Ferdinand Schmidt‐Kaler, Hartmut Häffner, S. Gulde, Mark Riebe, Gavin P. T. Lancaster, Jürgen Eschner, Christoph Becher, R. Blatt · Europhysics Letters (EPL) · 2004
A single 40 Ca + -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 S 1/2 to D 5/2 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.