Photon interference among distant quantum emitters was a promising method to generate large scale quantum networks. Interference was best achieved when photons show long coherence times. For the N-vacancy defect center in diamond, the coherence times of photons were measured via optically-induced Rabi oscillations. Experiments revealed a close to Fourier-transform (i.e., lifetime) limited width of photons emitted even when averaged over minutes. The projected contrast of 2-photon interference was 0.8. Twelve and 7.8ns excited state lifetimes were reported, depending upon the spin state of the defect

Temporal Coherence of Photons Emitted by Single Nitrogen-Vacancy Defect Centers in Diamond Using Optical Rabi-Oscillations. A.Batalov, C.Zierl, T.Gaebel, P.Neumann, I.Y.Chan, G.Balasubramanian, P.R.Hemmer, F.Jelezko, J.Wrachtrup: Physical Review Letters, 2008, 100[7], 077401