Quantum information processing in decoherence-free subspace with nitrogen-vacancy centers coupled to a whispering-gallery mode microresonator

We investigate the input–output process with nitrogen-vacancy (NV) centers fixed on the surface of microtoroidal resonators (MTRs) with quantized whispering-gallery modes (WGMs). We demonstrate a photon–NV hybrid controlled phase flip (CPF) gate in decoherence-free subspace (DFS) with the input–output process. Efficient schemes of entanglement generation and quantum state transfer (QST) in DFS are proposed. Our schemes removed the requirements of high-Q and strongly coupling for the physical systems, and DFS encoding makes our schemes immune to collective dephasing. The experimental feasibility and challenge are discussed by considering the current experimental technology.