Research On Quantum Noise And Off-diagonal Geometric Phase In Composite Systems

Quantum information is new-rising research including quantum mechanics and the theory of information, which is more advanced compared to classical theory of information. Some new quantum behavior is gradually confirmed in recent years, such as quantum entanglement, quantum teleportation and quantum non-locality, which accelerates the development of quantum information. Decoherence due to the interaction of quantum systems and environment is mainly difficult to application of quantum information. Environment is treated as noise in quantum information;generally speaking, it is negative for quantum information processing. However, we investigate whether it could achieve noise-assisted entanglement preparation or not.There are five chapters in the dissertation, which is mainly about quantum noise from 1st to 4th chapter, and off-diagonal geometric phase of composite systems is discussed in the last chapter. In the 1st chapter, it is an introduction to quantum noise. There is some research on entanglement preparation employing white noises in the following two chapters. We study steady state entanglement of atom-photon in cavity QED systems in the 4th chapter. In the first section we introduce the research results of Sun et al which studied the atom-photon entanglement preparation and distribution, and analyzed the role of the classical external field on atom-photon entanglement in cavity QED system. In the second section we extend the study on noise-assisted entanglement generation of the systems from atom-atom to atom-photon. It is of interest that the systems of atom-photon eventually evolved into a steady state. We show that noise may play a positive role in entanglement generation of atom-photon in cavity QED systems. The dependence of the entanglement on the noise intensity as well as the other parameters in the model is illustrated both analytically and numerically. Our results shed new light on the problem of noise-assisted entanglement preparation and on the entanglement generation in flying-localized qubit systems. In the last chapter we investigate off-diagonal geometric phase in composite systems.