Quantum Entanglement In Cavity Quantum Electrodynamics System

Quantum information science is the combination of quantum mechanicsand information science, which has grown up since the end of the 20th cen-tury. Based on the quantum property, the quantum information science promisesmany new schemes of quantum communications and quantum computing, suchas quantum cryptography, quantum teleportation, and the scheme of factoriza-tion of large numbers, etc.. As the important character of quantum mechanics,quantum entanglement is the key resource of implementing various quantum in-formation processes. In recent years, the theoretical and experimental researchabout quantum entanglement has become the focus of quantum physics and in-formation science. However, the decoherence of quantum systems is always abottleneck of blocking the progress of quantum information science. Therefore,how to prepare the steady quantum entangled state in the proper quantum sys-tem is an important research topic. At present, there are many quantum systemsfor realizing the entangled state,which mainly include cavity quantum elec-trodynamics (cavity QED) systems, trapped ions, electronics spin or nuclearmagnetic resonance,quantum dots and superconducting quantum interferencedevices (SQUIDs) etc.. Thereinto, cavity QED systems have the advantages ofsuppressing the decoherence and constructing the quantum network. Based onthis point, in this paper, we mainly research the entangled state preparation incavity QED systems. The main contents are as follows:1. Based on the atomic coherence induced by classical field, we proposethe scheme of generating two-mode continuous-variable entangled state in thesingle atom and single molecule magnets cavity QED systems. In addition, wealso analyze the corresponding entangled property between cavity modes, and the results show that the entangled property between two cavity modes can beadjusted effectively via changing the intensities of classical fields or frequencydetuning of system in our scheme.2. We extend the corresponding theory into the instance of multi-modeentanglement, and propose a new scheme for realizing three-mode continuous-variable entanglement in a cavity QED system. In addition, the in?uence ofclassical field intensity and system initial condition on the entanglement gener-ation also are discussed.3. First of all, we propose the schemes for realizing two-dimensional andthree-dimensional entanglement between two spatially separated atoms in thecoupled cavity-fiber-cavity systems, and analyze the in?uence of system decayon the fidelity of realizing entangled state. The numerical results show thatthe in?uence of system decay can be suppressed effectively in our scheme viaproperly choosing the atom-field detuning and cavity-fiber coupling intensity.Then, we extend the corresponding theory into the instance of multi-partite entanglement and propose a new scheme for realizing three-partiteGreenberger-Horne-Zeilinger (GHZ) state and W state in the coupled cavity-fiber-cavity systems based on the selective photon absorption and emission pro-gresses. In addition, we also discuss the in?uence of system parameters anddissipations on the fidelity of our scheme in detail.4. Based on the STIRAP, we propose a scheme for realizing the entan-glement between two spatially separated microwave cavities interacting withsingle molecule magnets. The advantage of this scheme is that the in?uenceof system dissipations can be neglected approximately, which increases theexperimental feasibility of this scheme. At the same time, we also analyze the?uctuating effects of some system parameters on the fidelity of our scheme.