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Theoretical Study On Preparation Of Entangled States And Their Applications In Quantum Communication

Posted on:2010-03-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y XiaFull Text:PDF
GTID:1100360275958059Subject:Theoretical Physics
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The quantum informatics is an intersection of quantum mechanics and information theory, arisen from 1980s.Over the last two decades,there has been rapid development in both theoretical and experimental studies on quantum information.Quantum entanglement is not only one of the major characteristics that distinguish quantum from classical mechanics, but also an essential ingredient of quantum information theory.As one of the most striking features of quantum formalism,quantum entanglement is used in the field of quantum information as an effective resource.The entanglement has involved many interesting applications without classical counterparts,such as quantum teleportation,quantum dense coding,remote state preparation,quantum secure direct communication,and quantum secret sharing.Therefore,the study of both quantum entanglement and its applications in quantum information theory are necessary and valuable not only to understand well the special properties of the quantum mechanics but also to develop and make use of the new information process methods.Taking the problems stated above into account,theoretical study on preparation of entangled states and their applications in quantum communication are mainly discussed in this dissertation.The thesis has been divided into seven chapters,and our works are included in the chapters from 3 to 7.In Chapter 1,the background of the study,the proposition and definition of quantum entanglement are introduced,and the major research subjects and the organization of the dissertation are given at the end of this chapter.In Chapter 2,the basic conception of quantum information is introduced.Firstly,EPR paradox and Bell inequality,and several kinds of entangled states,as well as their properties, are given.Then the measurement of the degree of quantum entanglement,quantum nocloning theorem,and manipulation of quantum entanglement are introduced.At last,several typical quantum information protocols are also introduced in order to demonstrate that quantum entanglement is an important physical resource.In Chapter 3,the protocol for generating Greenberger-Horne-Zeilinger(GHZ) state of N distant photons with linear optical elements is proposed.The proposed setup consist of simple linear optical elements,N pairs of the two-photon polarization entangled states,and the conventional photon detectors that only distinguish the vacuum and nonvacuum Fock number states.This makes the protocol more realizable in experiments.In chapter 4,the applications of entangled states in quantum teleportation is discussed and two theoretical protocols are developed.In the first protocol,an arbitrary N-qubit GHZ entangled state can be probabilistically teleported from the sender to the receiver via only one non-maximally two qubit entangled state.Without entanglement concentration,using standard Bell-state measurement and classical communication one cannot teleport the state with unit fidelity and unit probability.In the second protocol,an arbitrary and unknown two-qubit entangled state can be probabilistically teleported from the sender to the receiver via a one-dimensional four-particle non-maximally entangled cluster state.By construction, the four-particle state is not reducible to a pair of Bell states.In chapter 5,the applications of entangled states in remote state preparation is discussed and one theoretical protocol is proposed.In this protocol,one sender and one receiver case, and multiparty remote state preparation(That is two- or multi-party share a quantum state, and they want to remotely prepare it to the receiver) case are considered.In chapter 6,the applications of entangled states in quantum secret sharing is discussed. A protocol is proposed for multiparty quantum secret sharing via introducing auxiliary particles using a non-maximally entangled two-particle state without a Bell measurement first, and then two optical protocols are proposed for quantum state sharing of superposed coherent states and entangled states,respectively.In chapter 7,the applications of entangled states in quantum secret direct communication is discussed.A protocol is presented for controlled quantum secure direct communication that uses a 2-dimensional Greenberger-Horne-Zeilinger(GHZ) entangled state and a 3-dimensional Bell-basis state and employs the high-dimensional quantum superdense coding,local collective unitary operations and entanglement swapping.The proposed protocol is secure and of high source capacity.It can effectively protect the communication against a destroying-travelqubit -type attack.With this protocol,the information transmission is greatly increased. This protocol can also be modified,so that it can be used in a multi-party control system.Finally,the results are summarized at the end of the paper.
Keywords/Search Tags:quantum entanglement, linear optical elements, quantum secure direct communication, quantum teleportation, quantum secret sharing, remote state preparation
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