Continuous Variable Quantum Conference Network With Multipartite Entangled State

Large-scale conference networks are common in today’s society.With the development of the Times,the efficiency of web conference is recognized by a growing number of people,and the security is the focus.The security of classical communication relies on the complexity of mathematical problems,while the security of quantum communication relies on the basic principles of quantum mechanics.Quantum communication is unconditional secure communication in theory,so quantum communication has attracted wide interest.Since the security of quantum information is based on the basic principles of quantum physics,various communication protocols based on quantum information have been theoretically proposed and experimentally implemented,such as quantum key distribution(QKD),quantum teleportation,quantum dense coding,quantum secret sharing(QSS)and so on.In 1984,the first quantum cryptography protocol appeared,people realized the benefits and potential that quantum communication hold.QKD allows secret keys to be securely shared between only two remote users,while the ultimate goal of quantum communication is to build quantum communication networks,there are far more than two users involved.Quantum conference(QC)distribute the common key among many parties to realize the secure interaction of many users.The QC protocol is based on multipartite entanglement,which requires less quantum resources qubits and performs with fewer error correction and privacy amplification steps.The realization of these schemes will certainly promote the development of practical quantum information.The main contents of this doctoral dissertation are as follows:1.We use a nondegenerate optical parametric amplifier to generate quadrature amplitude and quadrature phase squeezed state,which contains the wedged KTP nonlinear crystal.The squeezed states prepared by two nondegenerate optical parametric amplifiers are interfered through different beam splitter networks,then the multipartite entangled state and bound entangled state can be produced experimentally.2.A four-user QC network scheme is proposed,which is based on continuous variable quadripartite entangled states.We analyze the conference key rate in a lossy quantum channel and study the security of QC network theoretically and experimentally.The deterministic QC network based on entangled state light field is realized experimentally.3.Considering that some users’ secret information is shared in the QC network,the communication will have a more secure key protection and management mechanism.We continue to study QSS,a secret means in the secure transmission of information.The QSS based on bound entangled states is proposed.We calculate the entanglement criterion of the bound entanglement state and preparation conditions theoretically,and the QSS of multi-users is realized.The key rate of different users of the threshold secret sharing is analyzed,the fidelity can also be adopted to characterize QSS.The creative works are as follows:1.The squeezed states prepared by two nondegenerate optical parametric amplifiers are interfered through beam splitter networks,the decoherence process can be simulated by coupling thermal noise,then the eight-partite bound entangled state is generated experimentally.2.Based on the inherent quantum correlation of the generated entangled state experimentally,the QC network can be realized which includes four users.Continuous variables secure communication between multiple users is realized.The secure key rate is analyzed under lossy quantum channel transmission theoretically and experimentally,and we analyze the security of QC network protocol when the collective Gaussian attacks exist.3.Eight-users QSS based on eight-partite bound entangled state light field can be realized.We theoretical analyze the implementation conditions of QSS based on bound entangled states and the key rate of threshold secret sharing with different number of users.