Generation of Greenberger-Horne-Zeilinger state of distant diamond nitrogen-vacancy centers via nanocavity input-output process

An alternative scheme is proposed for the generation of an N-qubit Greenberger-Horne-Zeilinger (GHZ) state with distant nitrogen-vacancy (N-V) centers confined in spatially separated photonic crystal (PC) nanocavities via input-output process of photon. The GHZ state is produced by the phase shift brought by the input-output photon. The certain polarized photon transmitted from a PC nanocavity side-coupled a waveguide can obtain different phase shifts due to the different spin states in diamond N-V centers and the optical spin selection rule. Our calculations show that the proposed scheme can work well with a large cavity damping rate which ensures the efficient output of photon.