Temporal coherence of photons emitted by single nitrogen-vacancy defect centers in diamond using optical rabi-oscillations

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 applications in quantum information processing. We report 12 and 7.8 ns excited state lifetimes depending on the spin state of the defect.