Photonic Entanglement States And Their Applications

Processing information with quantum mechanics, quantum information theorypromisesunconditionallysecurecommunicationandacceleratedquantumparallelismcom-putation, which also impacts the developing of quantum mechanics itself. Although ques-tions regarding entanglement and other fundamental issues of quantum theory still exist,entanglement has started to play important roles in information processing. Being an im-portantresource,quantumentanglementmakesmanynovelinformationprocessingproce-dures possible. Studies on the properties and applications of entanglement will definitelyenrichthetheoryofquantuminformationandpushitmoreclosertopracticalutility. Thosestudies can also help to clarify fundamental issues of quantum theory.Quantum entanglement has been achieved in many physical systems so far. Spon-taneous parametric down-conversion(SPDC) is the most developed as techniques for cre-ating photonic entanglement, which leads to significant experimental advances. In thisthesis, we focus on two photons created via SPDC, and dig into the properties and appli-cations of photonic entanglement. With photon pairs created under two kinds of phase-matching condition, we prepared two photons into polarization entangled states and per-formed Hong-Ou-Mandel interference experiments. Based on this, we considered appli-cations of photonic entanglement in quantum information processing and the studies offundamental problems in quantum theory.(1)We demonstrated an experiment for remote preparation of arbitrary photon polar-ization states. For arbitrary pure states, the efficiency is enhance to be 100%. Two-photonpolarization entangled state created via SPDC is employed as entanglement source. Weachieved remote preparation of 13 states with fidelities all above 0.994. The efficiency forarbitrary mixed states is also enhanced to be 100% in the modified scheme. This proposalcan also be used for remote preparation of states in other physical systems.(2)Employing single-photon two-qubit states, we experimentally implemented directcharacterization of one-qubit quantum dynamics(DCQD) on polarization states of pho-ton. Since Bell states measurement can be deterministically demonstrated, the quadraticadvantage of DCQD scheme is completely revealed.(3)For the first time, we proposed an experimental scheme to prepare and identify two-photon momentum positively-correlated entanglement state (MPES) via Hong-Ou-Mandel interference and direct projection measurements. Experimental data show thattwo photons are highly entangled with the transverse momenta of them positively corre-lated. Thus two-photon MPES has been achieved, and further investigations in proper-ties and applications of two-photon momentum entanglement become possible. The statetransformation and verification achieved here can also be used for kinds of operations andmeasurements on momentum entangled states.(4)A protocol for multiparty quantum secret sharing based on two-photon entangledstates was proposed. Preparation of multi-photon entangled states is no more necessaryand the risk from eavesdropper caused by the imperfection of the source is eliminated.Encoding with local unitary operations, many QKD protocols can be directly generalizedinto multiparty QSS ones.(5)An experiment is performed to observe the statistical correlations between pho-tons, which deepens our understanding of two-photon entanglement. From the results weconclude that two-photon state created via SPDC is an entangled state instead of a productstate under frequency-degenerate type-II collinear phase-matching condition.