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Experimental Manipulation And Application Of Two-photon States

Posted on:2010-12-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:W WuFull Text:PDF
GTID:1100360305473627Subject:Physics
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Exploring the rich variety of capabilities in information processing allowed by thenon-classical properties of quantum states (e.g. quantum superposition and quantum entanglement)is the subject of quantum information technology, which has become one ofthe most popular interdisciplinary fields.Entanglement lies at the heart of quantum mechanics. It has become a basic buildingblock for many novel quantum protocols, such as quantum key distribution, teleportation,dense coding and quantum computation. It is always a powerful tool that serves as akey resource for quantum communication and quantum computation. Then description,generation, manipulation and application of entanglement have became a very active fieldin theoretical and experimental quantum information science.Entangled states of various quantum systems have been investigated. To date, theirbiggest variety was observed in photonic qubit systems which is more feasible than others.So the first experiments of quantum key distribution, quantum teleportation and verificationof quantum nonlocality are realized with photonic qubits. The main part of this dissertationconcerns the experimental manipulation and applications of entangled photonsin quantum information science.Not all correlations between quantum systems, however, are purely quantum correlations(i.e. entanglement). People also find interests in the exciting subjects of characterizingother attractive types of correlations in quantum states. In general, there are quantumcorrelations, classical correlations and the mixture of them. In the last chapter, we makesome experimental studies about classical correlations.The main contents of this dissertation are as followsWe propose a scheme which can implement arbitrary positive operator-valued measures(POVM) on single-photon polarization state and is deterministic rather than probabilistic.With more feasibility in practice than former similar schemes, this scheme maybe used as a basic tool of various quantum information protocols in future applications.We experimentally demonstrate a kind of deterministic entanglement transformationsof bipartite pure states, which is the first experimental realization of non-trivial deterministicentanglement transformations. The average fidelity of all output states is 0.96. The protocol employs two-outcome POVM and can transform two-photon maximally entangledstate to any two-photon entangled pure state deterministically. Moreover, in principlewe can realize any kind of entanglement transformation of two-photon entangled purestates with the optimal theoretical upper bound efficiency.We experimentally demonstrate a protocol of probabilistic remote state preparationby virtue of entanglement, local operation and forward classical communications. Arbitrarypolarization qubit states can be remotely prepared with this protocol. The averageclassical information cost of successful remote preparation is calculated to be cbitper qubit by integrating this state-dependent cost. To our best knowledge, it is the lowestaverage classical information cost of successful remote preparation in all remote statepreparation experiments. All 18 remotely prepared states are estimated with quantum statetomography system, with average fidelity being 0.9956 and the minimal being over 0.99.By encoding the desired state into the spatial mode of single-photon, 100% efficiencyis obtained for the remote preparation of arbitrary single-photon pure polarization state.For mixed states, polarization insensitive measurement is introduced and the efficiency is50%. We achieve remote preparation of 13 states with fidelities all above 0.994.We propose a deterministic remote state preparation scheme for arbitrary photon polarizationqubit states, where entanglement, local operations and classical communicationare used. By consuming one maximally entangled state and two classical bits, an arbitrary(either pure or mixed) qubit state can be prepared deterministically at a remote location.We experimentally demonstrate the scheme by remotely preparing 12 pure states and 6mixed states. The fidelities between the desired and achieved states are all higher than0.99 and have an average of 0.9947. The methods used in our experiment can be generalizedto other situations. The operations on the photon can be utilized to remote controlother matter systems provided that the matter system is maximally entangled with singlephoton.Classically correlated states are experimentally prepared by introducing controlleddecoherence on the entangled photon pairs and the fidelity is 0.9915. We also proposeseveral ways to experimentally prepare classical correlated states with no entanglementinvolved at all. Then the first remote state preparation with no shared entanglement wasexperimentally demonstrated with classically correlated states. To estimate the performanceof our protocol, 42 qubit states are remotely prepared. The fidelities of all remotely prepared states are higher than 0.99.
Keywords/Search Tags:Spontaneous parametric down-conversion, Quantum entanglement, Two-photon states, Positive operator-valued measures, Entanglement transformation, Remote state preparation, Classical correaltions, Controlled decoherence
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