Efficient single-photon-assisted entanglement concentration for an arbitrary entangled photon pair with the diamond nitrogen-vacancy center insides cavity

In this paper, a protocol for single-photon-assisted entanglement concentration is proposed. Resorting to the nonlinear optics of a nitrogen-vacancy (NV) center in a diamond embedded in a photonic crystal cavity coupled to a waveguide, remote parties can share the maximally entangled photon pair with a certain probability. Compared with other entanglement concentration protocols (ECPs), the current one does not need to know the accurate coefficients of the initial state and can be repeated to get a higher success probability. Meanwhile, this protocol is more suitable for multiphoton system concentration. All these advantages make the protocol useful in long-distance quantum communication.