The Dissipation And The Decoherence In Cavity QED

Quantum Optics is an important branch of modern physics. Due to the development of Quantum Optics and the presently experiment technology, the basic idea and the basic law of Quantum Mechanics have been validated. The combination of quantum mechanics and information science results in the birth of quantum information. The schemes of quantum calculation and quantum communication via quantum optics are active topics up- to-date. Cavity QED as a candidate has been attracting much attention<, In the thesis, based on the research foundation of Jaynes-Cumming (JC) model, the dissipation and decoherence is studied via completely quantum theory. It is found: (1)The coherence property of the field is affected by cavity both qualitatively and quantitatively when two-photon processes and the Stark shift are taken into account. This is different from the one-photon process. (2)The original two-photon JC model is generalized to the case of degenerate atomic level. The quantum theory of degenerate two-photon JC model with and without rotating-wave approximation (RWA) is established. It is found that the revival period of degenerate JC model becomes longer and the maximum amplitude of atomic inversion decreases with RWA. Without RWA, quantum chaos of generalized JC model is much weaker than that of original JC model. The degeneracy of angular momentum can restrain the phenomenon of quantum chaos. (3) The dissipation of a degenerate-level atom interacting with a single linearly-polarized mode field in one-photon process as well as in the two-photon are studied. The degeneracy of the atomic level affects the dissipation of the system, of the atom and of the field. During the evolution, the atom and the field both are not in pure states. It is apparently different from the non-degenerate case. The quasiperiod is much longer than that of entanglement in the usual dissipative JC model in dispersive approximation. (4)According to the criterion of mixed state entanglement proposed by Peres and Ilorodecki, the entanglement of two atoms when they simultaneously interact with a single-mode thermal field is investigated. It is found that when the atoms initially in different state, they are entangled through interaction with the thermal field. It is shown that entanglement through nonlinear interaction is stronger than that through the linear interaction. The two criteria of mixed state entanglement arc also reviewed. (5)In the section 6, the two-mode field normal squeezing under .1C model including Stark shift is researched for the different values of superposition angle 6 and the relative phase p. In section 7, the chaos of atom population with and without RWA is investigated.