| In the last two decades quantum information theory has emerged as a branch of quantum physics which links concepts of quantum physics to ideas from information theory. Quantum entanglement is the crucial resources in the quantum information process. The concept of entanglement has been of great interest since the early days of quantum mechanics, and it has become important in many aspects of quantum information such as quantum teleportation, dense coding and quantum cryptography. Due to the promising applications of entanglement in quantum information science, the generation and manipulation of entanglement have drawn much attention. Therefore, the research on the quantum entanglement has significant both theoretical and practical values.However, how to design and realize quantum entanglement is extremely challenging due to decoherence. Various quantum systems have been suggested as possible candidates for engineering it. Among them the cavity QED system is an almost ideal system to generate entanglement between atoms or photons. In this thesis, we introduce some schemes of generating, manipulating and keeping the coherent characteristics of multipartite entanglement state in cavity QED system. The main contents are as follows: 1. We present a robust scheme for generating the multipartite entanglement of atoms utilizing"weakly driven approach"condition. The atoms are weakly driven by an external field and a leaking photon from one of the cavities is detected. The scheme uses cavity decay to inject photons into a setup of optical devices that consist of beam splitters and photon detectors. Photon detection on the output modes projects the atoms state onto multipartite entanglement state.2. Using atoms interaction with optical cavities, we describe a method of generating multipartite entanglement state of several separate cavities.3. We study the problem of how to keep coherent characteristics of multi-atom entanglement state in the cavity QED system. |
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