The Generation Of Quantum State And Implementation Of Entanglement State Analyzers Based On The Leaked Cavity

Quantum information science, a new cross knowledge, is the application of the quantum mechanic on information science. Due to its incomparable superiority compared with classical information science, qantum information science has been attracting great concern since it is found.The many advantages in quantum information come from the coherence of quantum system. However, decoherence induced from the system-environment unavoidably coupling will spoil the coherence.. One has to spend a lot of physical resources so that eliminates or reduces the effect of decoherence. Cavity QED, as one of promising physical systems to realize quantum information processing, has attracted significant interest. Because the inexistence of the perfect reflecting mirror, the photons finally leak out from cavity after the photons being reflected by cavity, which will cause the decoherence of the cavity system. To solve the problem, people design many exquisite schemes to restrain or avoid the decoherence resulted from cavity decay.Recent researches show that the decoherence induced from cavity decay can be seemed as a positive effect replacing a negative one by designing an appropriate dynamics, and it can be applied to quantum information processing. In this dissertation, we continue to investigate how to create or identify entangled states by using cavity decay. Our main results include:1. We propose schemes to generate a n-coherent-pulse GHZ state and a cluster state via a two-sided leaked cavity. In the schemes, the nonlinearity interaction among the input coherent pulses is achieved. The cavity involved inthe proposals is a two-sided cavity, which just is the practical cavity in current laboratory. And strong coupling condition is not required.2. Based on one-sided cavities each trapping an alkali atom, the schemes for the analyzers of two photon Bell states and three-photon Greenberger-Horne-Zeilinger (GHZ) states are proposed, respectively. Moreover, all of two-photon Bell states and three-photon GHZ states can be nondestructively distinguished. The influence of atomic spontaneous emission and output coupling inefficiency are discussed. 3. The schemes are presented for realizing optical Bell-state and GHZ-state analyzers through the Faraday rotation, which results from polarization photon being reflected by a one-sided leaked optical cavity with trapped atom. It can be extended to completely distinguish photon Bell-state and GHZ-state without destroying quantum qubit. In the schemes, strong-coupling condition is not needed and the analyzers can be implemented in low-Q cavity, which further lower the difficulties of experiment.