High-fidelity ion-trap quantum computing with hyperfine clock states
Leandro Aolita, Kihwan Kim, Jan Benhelm, Christian F. Roos, Hartmut Häffner · Physical Review A · 2007
We propose the implementation of a geometric-phase gate on magnetic-field-insensitive qubits with ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\sigma}}}^{z}$-dependent forces for trapped ion quantum computing. The force is exerted by two laser beams in a Raman configuration. Qubit-state dependency is achieved by a small frequency detuning from the virtually excited state. Ion species with excited states of long radiative lifetimes are used to reduce the chance of a spontaneous photon emission to less than ${10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}\mathrm{per}$ gate run. This eliminates the main source of gate infidelity in previous implementations. With this scheme it seems possible to reach the fault-tolerant threshold.