Here in this study we propose an efficient entanglement concentration protocol (ECP) for separate nitrogen-vacancy (NV) centers, resorting to the single-photon input---output process of the NV center and microtoroidal resonator coupled system. In the proposed ECP, one ancillary single-photon is prepared and passed through a hybrid quantum circuit. By measuring the photon under the suitable polarization basis, maximally entangled state between the separate NV centers can be obtained with a certain success probability. The solid entanglement will be preserved during the process, which can be iterated several rounds to obtain an optimal total success probability. We also discuss the experimental feasibility of the protocol by considering current technologies, and we believe that the protocol is useful in the future applications of long-distance quantum communication and distributed quantum computation.
The concatenated Greenberger-Horne-Zeiglinger (C-GHZ) state which is a new type of logic-qubit entanglement has attracted a lot of attentions recently. We present a feasible entanglement concentration protocol (ECP) for logic-qubit entanglement. This ECP is based on the linear optics, and it does not know the initial coefficients of the less-entangled C-GHZ state. This protocol can be extended to arbitrary C-GHZ state. This protocol may be useful in future quantum information processing tasks.
Since the end of the Cold War, the study of European defence has been dominated by a ‘Common Security and Defence Policy (CSDP)-centric’ approach, while largely neglecting the comparative analysis ...