Two-photon quantum interference from separate nitrogen vacancy centers   in diamond
  We report on the observation of quantum interference of the emission from two separate nitrogen vacancy (NV) centers in diamond. Taking advantage of optically induced spin polarization in combination with polarization filtering, we isolate a single transition within the zero-phonon line of the non-resonantly excited NV centers. The time-resolved two-photon interference contrast of this filtered emission reaches 66%. Furthermore, we observe quantum interference from dissimilar NV centers tuned into resonance through the dc Stark effect. These results pave the way towards measurement-based entanglement between remote NV centers and the realization of quantum networks with solid-state spins. 
Hannes Bernien, Lilian Childress, Lucio Robledo, Matthew Markham,   Daniel Twitchen, and Ronald Hanson
quant-ph cond-mat.mes-hall