Quantum Logic Gates And Their Applications Based On Nitrogen-Vacancy Centers In Diamond

Quantum information theory, combining mechanics and information science, is a new subject of great potential. Great efforts have been devoted into this area theoretically and experimentally. To realize quantum information processing tasks, we need to manipulate the quantum states, so quantum logic gate is a basic block in quantum information processing (QIP). On the other hand, feasible physical sys-tems are essential to realize QIP. Presently, there are several physical systems have potentials to realize quantum information processing, such as cavity quantum elec-trodynamics, nitrogen-vacancy (NV) centers, superconducting Joseph junctions and so on. Each of the systems has their own.advantages and disadvantages. Partic-ularly, NV centers in diamond, for their long coherence time in high temperature and favourable controllability, has attracted much attention. The aim of this thesis is to design simple schemes for implementation of quantum logic gates based on the present experimental technology. And then, use the logic gates, we study the entanglement-generation and the realization of quantum cloning.Base on NV centers in diamond, the main contents are as follows:We analyze the input-output relation in a composite system consists of two NV centers fixed on the surface of an microtoroidal resonators (MTR), with the build-ing block, a hybrid controlled phase flip (CPF) gate is constructed, entanglement generation and quantum state transfer can be realized in decoherence-free subspace (DFS). 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.Second, we propose a quantum CPF gate based on a nitrogen-vacancy ensemble-superconducting flux qubit (NVE-FQ) coupled system, we show the cluster states can be efficiently generated using the CPF gate. Because of the adoption of NV ensemble instead of single NV center, the CPF operation can be greatly speeded up. Analyses on the influences of dissipation show that this gate is robust.At last, we propose a scheme of an iSWAP gate between two NV centers located in two spatially separated nanocavities in a planar photonic crystal (PC). Use this gate, we designed quantum circuit and physical implementation for the optimal asymmetric (symmetric) 1 â†' 2 universal quantum cloning, the optimal symmetric economical 1â†'3 phase-covariant cloning and the optimal asymmetric (symmetric) real state cloning. The analysis results show our scheme is efficient and may be useful for scalable quantum information processing.All the schemes are scalable and feasible with currently experimental technol-ogy, so they are useful for QIP in the future.