Multipartite entanglement concentration for nitrogen-vacancy center and microtoroidal resonator system

We describe a high efficient entanglement concentration protocol (ECP) for multi-particle less-entangled nitrogen-vacancy (N-V) center and microtoroidal resonator system. In the ECP, we only require one pair of less-entangled state, two auxiliary N-V center in microcavities and some single photons. After the photon passing through the microcavity, by measuring the polarization of the photon, a maximally entangled W state can be obtained with some success probability. This ECP does not need to destroy the solid qubit, which makes it more feasible. Moreover, by resorting to more single photons, it can be repeated to reach a high success probability. These features make this ECP useful in current long-distance quantum communications.