Effective W-state fusion strategies in nitrogen-vacancy centers via coupling to microtoroidal resonators

We propose effective W-state fusion schemes for nonlocal electron-spin states and photon states by using the nitrogen-vacancy centers defect in diamond coupled to microtoroidal resonators. Using these schemes, a (m+n-1)-qubit W state can be obtained by fusing n-qubit and m-qubit W states (m, n ≥ 2), which means these schemes are applicable to create arbitrary scale W states with Bell states as the initial resource. The construction of these schemes is very compact and simple compared with the previous logical-gate-based fusion schemes. We analyze the feasibility and evaluate the optimal resource cost of the schemes, which shows that the present schemes can be realized with high fidelities and less resource cost than the previous schemes. Our schemes may be significant for the large-scale solid-state-based entanglement generation and for photon-qubit-based quantum information processing tasks.