The Physical Realization For Quantum Entanglement

Quantum information science is the combination of quantum mechanics and information science. This combination has injected new vigor and vitality into the information science. At the same time, it also greatly enriches quantum theory, and helps to solve some problem that the classic information science can not explain.Entanglement states, especially multi-particle entanglement states (such as GHZ state and cluster state), arc the crucial ingredients in many quantum information process. The cavity QED system and the trapping ion technology are two ideal physical implementation systems for quantum information processing. So implementation of entanglement states based on the cavity QED system and the trapping ion technology is of great theoretical and practical significance. The main contents of this dissertation are as follows:1. Several robust schemes are proposed to prepare entangled states among spatially separated A -type atoms via Stimulated Raman adiabatic passage and fractional Stimulated Raman adiabatic passage techniques. In the schemes for creation of atomic entanglement states, the fiber mode, the cavity mode, and the atomic excited states are never appreciably populated, so these schemes are free of the effects of the atomic spontaneous emission, the cavity decay, and the fiber loss. The effects of the experiment parameter error on the proposals are discussed. The schemes can be extended to generate the n-cavity mode W state.2. We propose a scheme for speedily producing entangled state for many trapped ions. In the scheme the ions are driven by a standing-wave laser beam, whose frequency is tuned to the ion transition. Mediated by the collective ion vibrational mode, we can realize a long-range interqubit coupling, based on which the entangled multi-ion state can be efficiently generated. Our scheme is insensitive to heating of vibrational motion. Remarkably, the required operation time is greatly decreased, which is important in view of decoherence.3. We propose schemes to prepare n-atom Greenberger-Horne-Zeilinger (GHZ) state via two-sided cavities interacting with single-photon pulses, and achieve quantum state transfer (QST) from one atom to another atom. Entanglement particle pair and the control of coupling between qubits arc of no need in the QST process. Some practical quantum noises only decrease the success probabilities of the schemes but have no influence on the fidelity of prepared state. In addition, the success probabilities of our schemes are close to unity in the ideal case.