Quantum Manipulation In Coherent Media

Quantum information science, as a cross-disciplinary field of quantum me-chanics and information science, has exploded into virtually every area of mod-ern physics because of the promise it holds for understanding physical limits to communication, computation and more generally the processing of information. Entanglement is an essential resource in quantum information science. It has been widely used in quantum computation, quantum communication and quantum cryp-tography, etc. Recently, manipulation and generation of entangled state, as well as some other manipulation on quantum state, have become the focus of quan-tum physics and information science. Nowdays, many systems can give a feasible platform to study quantum manipulation, such as cavity quantum electrodynam-ics (cavity QED) systems, nuclear magnetic resonance systems, quantum dots, trapped irons, among which the cavity QED is one of the most promising design of quantum hardware because of its advantage in suppressing decoherence. Based on this, quantum manipulation in cavity QED systems is investigated in this disserta-tion, including the generation of entangled state of atoms, quantum state transfer between two spatially separated qubits. The main contents are as follows:1. A new scheme is proposed to achieve fully tripartite entanglement in a four-level atomic system driven by two strong classical fields. Via numerically simulating the dynamics of the system, we investigate the generation and evolu-tion of entanglement. Based on our scheme, it is demonstrated that the tripartite continuous-variable entanglement can be achieved under different initial condi-tions and the entangled periods will be extended by enhancing the intensity of the classical field. Moreover, our numerical results also show that the present system can be considered as a tripartite entanglement amplifier.2. Based on the adiabatic passage along dark states, we propose two schemes for generating GHZ and W states of three distant atoms. In the present schemes, the atoms are individually trapped in three spatially separated optical cavities cou-pled by two optical fibers. The populations of cavities and fibers being excited can be negligible under certain conditions. In addition, the spontaneous decay of atoms is also efficiently suppressed based on our proposals. Furthermore, some discus-sions about the entanglement fidelity are given and we point out our schemes work robustly with small fluctuations of experimental parameters.3. We propose a new scheme for realizing deterministic quantum state trans-fer between two spatially separated single molecule magnets with the framework of cavity quantum electrodynamics (QED). In the present scheme, two SMMs are trapped in two spatially separated optical cavities coupled by an optical fiber. Through strictly numerically simulating, we demonstrate that our scheme is robust with respect to the SMMs'spontaneous decay and fiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber. In addition, we also discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate the generation of QST with high fidelity utilizing the current experimental technology. The present investigation provides research opportunities for realizing QST between solid-state qubits and may result in a substantial impact on the progress of solid-state-based quantum communications network.