| Established in the beginning of the twentieth century, still in development, quantum mechanics is significantly deepening the understanding of our natural. One aspect is that the basic problems of the theory, such as foundations and principles of quantum mechanics, have no conclusion accepted by academia so far. On the other hand, the application of quan-tum mechanics are increasing widely. As we know, quantum mechanics occupies a leading role in the world of micro scale material structure, especially in the area of atomic physics, solid physics, nuclear physics and quantum information. As an emerging discipline attracted significant interest, quantum information theory has got much attention from scholars for it has wide research field and important application prospect, and it is also a new cross subject of quantum theory and information science. Meanwhile, it widely enriches the research field of quantum theory and helps us to have a better understanding of the essence of quantum theory. Dominated by quantum mechanics, the world of quantum information takes a new look and shows some distinguished advantages compared with classical information. Quan-tum entanglement is a nonlocal correlation, it is becoming an important research field both in theory and experiment. The preparation of continuous-variable (CV) entanglement states are acting on a frontier field in quantum optics, this is mainly because CV quantum commu-nication have excellent performance in detection efficiency, bit rate and communication band. Therefore, the research on CV communication network has wide application in the future. This thesis mainly discuss the effect of nonsecular terms of a V-type system in momentum representation, the Hamiltonian of which both beam splitter (BS) and nondegenerate para-metric down conversion (NPDC) terms appear. The pure state solution of wave function enables us to fully discuss the dynamics and entanglement properties of our system. By tracing over the environment degrees, we obtain a master equation of the system and show that the effect of the quantum interference resulted from the two atomic decay pathways can lead to spontaneous emission quenching. If the loss of the cavity is extremely small, the pure entangled state can be obtained under the condition of spontaneous emission quenching. Even if the cavity loss cannot be ignored, the quenching of spontaneous emission can help us to decrease the dissipation from the environment.The content of this article can be broadly divided into four chapters. In chapter1, the basic theory of quantum information and quantum optics are introduced, including the measurement of quantum entanglement, the basic of cavity QED system and the concept of CV entanglement which we are especially focused on. chapter2shows the rudiments of the interaction between atom and field, including the quantization of the electromagnetic field, the quantum theory of the interaction between atom and field. In chapter3. the theory of IWOP (integration within an ordered product) technique is introduced. Last chapter is our main work. A scheme generating entangled coherent states by using V-type atom-cavity system is presented in this chapter. When nonsecular approximation is employed, we find that nonsecular terms, although small, can have a significant effect on the entanglement properties, and we also give a pure state solution in wave function to describe it. In the presence of cavity losses and atomic relaxation, we show that complete quenching of spontaneous emission is possible under appropriate conditions. Therefor, reduce an adverse impact from decoherence process. |
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