Quantum gate using qubit states separated by terahertz
Kenji Toyoda, Shinsuke Haze, Rekishu Yamazaki, Shinji Urabe · Physical Review A · 2010
A two-qubit quantum gate is realized using electronically excited states in a single ion with an energy separation on the order of a terahertz times the Planck constant as a qubit. Two phase-locked lasers are used to excite a stimulated Raman transition between two metastable states ${D}_{3/2}$ and ${D}_{5/2}$ separated by $1.82$ THz in a single trapped $^{40}\mathrm{Ca}$${}^{+}$ ion to construct a qubit, which is used as the target bit for the Cirac-Zoller two-qubit controlled NOT gate. Quantum dynamics conditioned on a motional qubit is clearly observed as a fringe reversal in Ramsey interferometry.