| Quantum communication and quantum cryptography is a subject which combines traditional cryptography and quantum mechanics. It provides an optional new method for information security. Different from traditional cryptography which based on the assumed difficulty of mathematical problems, the security of quantum cryptography is based on Heisenberg uncertainty principle and quantum no-cloning theorem. Quantum cryptography not only has proven security and also can be detected if eavesdropping has occurred. Compared with other cryptography schemes, these are specific characteristic, which has an important application prospect and far-reaching significance.In this thesis, some questions of the quantum cryptography communication have been explored and studied, such as quantum key distribution, quantum secret sharing, quantum controlled teleportation, quantum secure direct communication and so on. The main works done are listed as follows.First, according to the structure of European Secoqc QKD network, a quantum key distribution protocol is proposed based on entanglement swapping, and random space quantum channel selection to improve the probability of revealing Eve. The protocol proposed exhibits the following features. It is proper to mesh QKD network structure. And it can be generated using the less quantum resource. Detecting Eve requires the comparison of fewer bits.Secondly, a multi-party quantum state sharing protocol is suggested by using entanglement swapping and random EPR selection. The EPR pairs of Bell-state measurement are selected randomly by the sender which can improve the security of the scheme and raise probability of detecting Eve. In addition, difference coding is used in this protocol to achieve a high efficiency. It is convenient in application as it require less quantum resource.Third, a scheme for teleporting multi-qudit quantum state is presented, via many controllers, based on Bell-state entanglement swapping. The presented scheme is the qudit case of controlled teleportation protocol, whose control parameters are obtained using entanglement swapping of maximally d-dimensional EPR pair. The scheme of multi-qudit owns the advantage of having higher code capacity and better security than that of multi-qutrit or multi-qubit. Four, a multiparty controlled secure quantum communication of d-dimensional is proposed based on GHZ state and teleportation. After using decoy photons to check eavesdropping efficiently for the purpose of the quantum channel security, the sender encodes the secret message of d-dimensional on a sequence of additional particle states and then fulfills teleportation of the secret through d-dimensional Bell state measurement and X-basis or Z-basis measurement.Five, a scheme for probabilistic controlled teleportation of a triplet W state using combined non-maximally entangled channel of EPR and GHZ is given. In this scheme, the GHZ state serves not only as the control parameter but also as quantum channel. The total probability of successful teleportation is only dependent on channel coefficients of EPRs and GHZ, independent of the number of supervisors. And it is extended to the arbitrary n-qubit quantum controlled transmission using the mixed-channel.Six, we explicitly present a general scheme for controlled quantum teleportation of an arbitrary multi-qudit state with unit fidelity and non-unit successful probability using d-dimensional nonmaximally entangled GHZ states as the quantum channel and generalized d-dimensional Bell states as the measurement basis. The expression of successful probability for controlled teleportation is present depending on the degree of entanglement matching between the quantum channel and the generalized Bell states. And the formulae for the selection of operations performed by the receiver are given according to the results measured by the sender and the controller. Finally, the scheme is extended to the mixed EPR and GHZ channel to further reduce the quantum of resources costs.
|
PDF Full Text Request