A concept which combined optics and microwave pulses with the negative charge-state of the N-vacancy (NV-) center was demonstrated by experiments that were equivalent to single-qubit gates. The spin levels of the ground state provided a 2-level system, and optical excitation provided polarization of the states. The polarized state was operated coherently by 35GHz microwave pulses. The final state was read from the photoluminescence intensity. Decoherence arose from different sources in different samples. In high-pressure high-temperature synthetic diamond, the high concentration of substitutional N limited the phase-memory to a few μs. In monocrystalline chemical vapour deposited diamond, the phase memory time was at least 32μs at 100K, and 14N was tightly coupled to the electronic spin and produced modulation of the electron-spin

echo decay under certain conditions. A 2-qubit gate was proposed which used this nuclear spin.

Single-Qubit Operations with the Nitrogen-Vacancy Center in Diamond. T.A.Kennedy, F.T.Charnock, J.S.Colton, J.E.Butler, R.C.Linares, P.J.Doering: Physica Status Solidi B, 2002, 233[3], 416-26