Study On The Preparation Of Graph States And Quantum Decoherence

Based on superposition state principle of quantum mechanics, quantum in-formation science, which combines quantum mechanics with information science, is a new and front subject about quantum information processing. In recent years, The research of quantum information science has achieved significant progress about quantum cloning, quantum error correction, quantum teleportation, quantum dense coding both in theory and experiment. In quantum information processing, storing, denoting and extracting of information are dependent on quantum states and their evolution. Because quantum entanglement is associated with the unique quantum correlations, it plays an important role in quantum information processing. How-ever, quantum decoherence will appear when the carrier of information unavoidably interacts with its environment in the process of information transmitting and pro-cessing, which can result the loss of information. So, quantum entanglement and quantum coherence are important resources of quantum information. Thus, the problems about how to prepare entangled state, control the evolution of quantum state and keep quantum coherence have become the most important subject of quan-tum information theory. As is well-known, multi-qubit entangled states have more advantages than two-qubit entangled states in their applications in quantum cloning, teleportation and dense coding, and are essential resources for quantum computing and quantum information processing. In this paper, we propose theoretical schemes for preparing a kind of special pure multi-qubit entangled states——graph states by using spin networks, and preliminarily investigate entanglement dynamics under non-inertial system.Graph states correspond to mathematical graphs and many entanglement prop-erties of graph states are closely related to their underlying graphs. In this paper, we propose an efficient scheme for preparing multi-qubit graph states via spin net-works. The classical types of graph states including cluster state, Greenberger-Horne-Zeilinger state and so on can be generated using imaginary SWAP gate through XY interaction. Our method makes the generation of multipartite entan-gled graph states more efficient than the ones based on conventional controlled-NOT and controlled phase flip gate for solid-state devices.Because quantum decoherence can destroy quantum entanglement, improving our understanding on entanglement dynamics and properties is necessary for ma-nipulating entanglement and resisting the influence of decoherence. Therefore, the research about how to keep quantum coherence is an important subject of quantum information theory. Here we investigate the quantum decoherence of Dirac fields in a non-inertial system under phase damping channel. The quantum decoherence and the loss of entanglement generated by Unruh radiation will influence each other. However, the difference between the amplitude damping channel and phase damping channel is that the entanglement disappears only as time tends to infinity (tâ†'∞) whether one or two qubits of system is coupled to the environment.