Proceeding Quantum Information Processing In Coupled Cavity QED System

Quantum information has been focus of science research since the1980s. Because the characteristics of coherence, entanglement and additivity in quantum mechanics, information can be stored, transferred, and computed by means of quantization to achieve the goal of quantum key distribution, quantum communication, quantum computing. There are many physical carriers to realize quantum information processing (QIP). Among these, cavity QED system can realize QIP by the interaction of atom and photon. The system has excellent anti-decoherence since the interaction time of atom and photon is smaller than their lifetime in cavity and thus has been extensively reaearched in theory and experiment recent decades. Especially, this system becomes a valuable candidate for practical QIP in the future because of the successful development of cavity with super high quality in recent years. On the other hand, the so-called distributed QIP that makes multi-cavities coupled is the development trend of future for the needs of addressing and anti-interference. Therefore, the quantum information processing based on coupled cavity QED system is our main work. In this paper, we discusses the generation of quantum states, the realization of quantum states transfer and quantum logic gate in coupled cavity QED system respectively. This thesis consists of seven chapters and our main research content is from chapter four to chapter seven. The detailed content is as following:In Chapter one, we introduce the background and main application of quantum information firstly, and then give a brief introduction of cavity QED system.In Chapter two, we introduce the basic knowledge and concepts of quantum information, including the picture concept, qubit, density operator, density matrix, quantum logic gate, entanglement and fidelity.In Chapter three, the theories of cavity QED system are introduced, including Jaynes-Cummings short fiber approximation theory and the Hamiltonian model coupled with environment.In Chapter four, we propose two schemes to one-step generate the three-particle Greenberger-Horne-Zeilinger state in the corss coupled cavities. In contrast with other proposals, our schemes are simple and efficient. Especially? the second scheme is equal to entangle two atoms in a cavity to acertain extent, and which has been implemented in experiment.In Chapter five, we present a scheme for realizing transfer of a three-dimensional (3D) quantum state between two atoms trapped in distant cavities connected by an optical fiber based on the atom-cavity resonant interaction. In contrast with the one based on the case of large detuning, it is shown that the higher fidelity can be achieved in the same dissipation parameters. Meanwhile, our scheme can be used to realize quantum phase gate by freezing atomic level. Besides, we improve the previous scheme which transfers quantum information by means of large-detuning in order to transfer quantum information of two atoms at one step.In Chapter six, we propose a scheme of transferring high fidelity three-dimensional quantum states in a cavity-fiber-cavity system. By employing atomic ensembles in a cavity and large-detuning interaction between atoms and photons, the interaction time can be shortened greatly and the atomic spontaneous emission can be ignored.More over, we propose a scheme for generating high fidelity three-dimensional entangled state for two atomic ensembles in cavity-fiber-cavity system. Our scheme provides the means for observing entanglement at a broader scale, and in addition, it would be close to high-fidelity in current parameters.In Chapter seven, considering the scale of generating entangment state is from microcosmic to mesoscopic and even macroscopic progressively in cavity QED system and other ones, we focus on two atomic ensembles which entangled each other as a whole. By assuming an entanglement model, we calculate the concurrence and negativity between subsystems. Our research provides a new way of studying entanglement and gives some prospective questions in last.