LAUSR

We investigate two schemes of direct concurrence measurement for two-qubit spin Werner states via the cavity-assisted interaction between single-photon pulses and nitrogen-vacancy centers in diamond. The first scheme requires multiple copies of initial Werner states but has no need of sophisticated controlled-NOT gate. The second scheme, as a resource-conserving one, adopts a kind of hybrid controlled-NOT gate between spin and photonic qubits but only needs one single copy of initial states. Both schemes get the concurrence in nondestructive ways, and the initial entangled states can be possessed by spatially separated participants. The final analyses show that the presented schemes are feasible under current experimental conditions and have reliable performance with imperfect initial parameters and operating processes.