| Quantum information science is a new cross subject which merges several subjects such as quantum mechanics, computer science, information theory. It is also a novel and promising research field now. This subject develops rapidly both in theory and experiment. Its birth and development not only strongly promote quantum theory, but also greatly change the way of information transformation and information processing. In addition, the phenomenon of entanglement is one of the typical features of quantum mechanics, and it is the important resources of quantum information and computation. We divide quantum information into two types as discrete variables (DV) and continuous variables (CV) according to the eigenstates of applied quantum systems, which are with discrete or continuous spectrum construetion. Each of them has its features, and has its advantages and disadvantages. They also play important roles in quantum information science. At first, quantum information is studied form DV, then extended into the field of CV. Comparing with other systems, the CV system has its own advantages, such as high bit transmission rates and high detection efficiency. So it has attracted wide interests. In addition, cavity QED, which discusses dynamic process of material interacting with electromagnetic fields inside a cavity, has been developed rapidly and relatively maturely. In this thesis, theoretical study on the quantum information transfer between atomic qubits and CV systems and the generation of cluster-type entangled coherent states and the non-classical state of atomic ensemble are mainly discussed in the system of cavity QED. The experimental feasibility is also discussed. The thesis has been divided into five chapters, and introduction is introduced in chapter1, basic knowledge of quantum information is introduced in chapter2, our works are included in the chapter3, chapter4and chapter5. The full thesis is organized as follows:In chapter1, the generation background and the research overview of quantum informa-tion science are briefly introduced, as well as the application prospects of continuous variable quantum entanglement and cavity QED are briefly discussed. Finally, the organization of this text is given.In chapter2, basic knowledge of quantum information is introduced. The basics of quantum mechanics firstly, the basic theories and concepts of quantum information are briefly reviewed. Finally, the quantum theory of the interaction between atom and field in quantum optics which relates to the thesis are described.In chapter3, a scheme is proposed about the quantum information transfer between atomic qubits and continuous-variable systems. The information carried by atomic qubits can be stored into cavity fields by introducing classical fields, and the deposited information can also be retrieved from the cavity fields to the atomic qubits by turning off the classical fields. Due to the maximum entanglement state is difficult to maintain, when we need to encode information, we usually employ non-equal superposition state rather than the maximum entanglement one. In addition, postselection projections is difficult to manipulate in experiment, and we choose homodyne detection and find out the error probability is very small.In chapter4, a scheme is presented for generating cluster-type entangled coherent states via cavity QED. The scheme is based on the off-resonant interaction between the atom and cavities, so the spontaneous emission of atom can be ignored. The initial states of the cavities are all prepared vacuum states. We also discuss the experimental feasibility.In chapter5, a scheme is proposed for generating the non-classical state of atomic en-semble. In this scheme, the atomic ensemble is trapped in a cavity, then squeezed vacuum state and squeezed coherent state of the atomic ensemble are prepared by choosing different initial state of the system.Finally, the results are summarized and the future research work are outlined. |
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