  Photon interference among distant quantum emitters is a promising method to
generate large scale quantum networks. Interference is best achieved when
photons show long coherence times. For the nitrogen-vacancy defect center in
diamond we measure the coherence times of photons via optically induced Rabi
oscillations. Experiments reveal a close to Fourier transform (i.e. lifetime)
limited width of photons emitted even when averaged over minutes. The projected
contrast of two-photon interference (0.8) is high enough to envisage the
applications in quantum information processing. We report 12 and 7.8 ns excited
state lifetime depending on the spin state of the defect.
