title: Direct measurement of nonlocal entanglement of two-qubit spin quantum states.
abstract: We propose efficient schemes of direct concurrence measurement for two-qubit spin and photon-polarization entangled states via the interaction between single-photon pulses and nitrogen-vacancy (NV) centers in diamond embedded in optical microcavities. For different entangled-state types, diversified quantum devices and operations are designed accordingly. The initial unknown entangled states are possessed by two spatially separated participants, and nonlocal spin (polarization) entanglement can be measured with the aid of detection probabilities of photon (NV center) states. This non-demolition entanglement measurement manner makes initial entangled particle-pair avoid complete annihilation but evolve into corresponding maximally entangled states. Moreover, joint inter-qubit operation or global qubit readout is not required for the presented schemes and the final analyses inform favorable performance under the current parameters conditions in laboratory. The unique advantages of spin qubits assure our schemes wide potential applications in spin-based solid quantum information and computation.
authors.affiliation: School of Physics and Information Engineering, Shanxi Normal University, Linfen, Shanxi 041004, China.
authors.forename: Liu-Yong
authors.initials: LY
authors.lastname: Cheng
authors.affiliation: School of Physics and Information Engineering, Shanxi Normal University, Linfen, Shanxi 041004, China.
authors.forename: Guo-Hui
authors.initials: GH
authors.lastname: Yang
authors.affiliation: Department of Physics, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Guo
authors.affiliation: Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002, China.
authors.forename: Hong-Fu
authors.initials: HF
authors.lastname: Wang
authors.affiliation: Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002, China.
authors.forename: Shou
authors.initials: S
authors.lastname: Zhang