Electron-spin echo experiments revealed phase-memory times which were as long as 58μs at 300K for N-vacancy centers in chemical vapor deposited single crystals. The spins were optically polarized and optically detected. Two high-quality chemical vapor deposited samples were studied. However, from these results, it was unclear whether the phase-memory times represented a fundamental limit or were limited by an external source of decoherence.

Long Coherence Times at 300K for Nitrogen-Vacancy Center Spins in Diamond Grown by Chemical Vapor Deposition. T.A.Kennedy, J.S.Colton, J.E.Butler, R.C.Linares, P.J.Doering: Applied Physics Letters, 2003, 83[20], 4190-2