Quantum Information Processing In Linear Optical System

Quantum information science is new inter-discipline generally covering quantum communication and quantum computation, Quantum communication is an important branch of the Quantum information science, the research of Quantum communication including quantum dense coding, quantum teleportation and quantum cloning. After the research of many years by physicists, people have acquired a series of important achievement. And this subject becomes one of the hotspot in international leading edge.There are many physical systems for implementing quantum information processing at present, such as cavity, molecule nuclear magnetic and so on. Quantum electrodynamics photon systems are prominent candidates, since they provide many advantages, such as long decoherence time, photons being easily transported, prepared and manipulated. Therefore, it is a very promising subject to deal with quantum information processing using the optical system. This paper has done some research on how to deal with the processing of quantum information in linear optical systems. We have achieved the following results:1. Scheme for implementing quantum dense coding by using linear optical systemA novel scheme for realizing dense coding with Greenberger-Home-Zeilinger (GHZ) state in linear optical system is proposed. In this protocol, Alice codes on photon 1 and 2 by linear optical element and sends these photons to Bob. Then Bob will perform a joint measurement on photons 1,2, and 3 with the GHZ basis by employing two quantum nondemolition detectors (QND) and polarizing beam splitter (PBS). Eight GHZ states can be completely discriminated. According to the outcomes of his measurement Bob can determine which operation Alice applied. Alice only transmits two photons in this process of the quantum dense coding, but Bob can obtain three bits of classical information. The QND devices are generally based on cross-Kerr nonlinearities, and the cross-Kerr nonlinearities have become available with electromagnetically induced transparency (EIT). 2. Linear optical scheme for implementing the optimal real state cloningWe propose an experimental scheme for implementing the optimal 1→3 real state cloning via linear optical elements. This method relies on one polarized qubit and two location qubits and is feasible with current experimental technology.