Study On Quantum Cryptography Communication Schemes And Transmission Characteristics Of Quantum Channel

With the maturation of discrete-variable quantum cryptography technology, theresearchers proposed continuous-variable quantum cryptography, which has the meritsof the low cost, simple generation and detection of quantum signals, and high secretkey rate. Thus this technology has favorable prospect of application. The foundationin information security of quantum cryptography communication is quantum informa-tion theory, in which the important issue is quantum channel theory, and the studiesare almost limited in memoryless and bipartite transmission channels. However, therealways exist some memory effects in the practical quantum channels. And quantumnetwork communication is the development trend of quantum cryptography commu-nication. So studies on the capacities and the influence on information transmissionof memory quantum channels, multi-access quantum channels and quantum networkhave fundamental significance for the development of communication security andquantum channel theory.In this dissertation, we study the design of novel continuous-variable quantumcryptography schemes and their practical securities, quantum capacities of quantumchannels and their non-additivities, the influences on the information transmission forspecial discrete-variable quantum channels, and the simulation and realization of spe-cific quantum channel. The main results are listed as following:1. A novel method is proposed to improve the performance of Gaussian modulationcontinuous-variable quantum key distribution (CVQKD) by using non-Gaussianoperations. In particular, the one-photon subtraction operation is analyzed. An-alytical results show that the non-Gaussian operations can increase the entangle-ment degree of entanglement source, i.e., the two-mode squeezed vacuum state, in the entanglement-based scheme of the CVQKD protocol, thus efficiently im-prove the maximum transmission distance and tolerable channel excess noise.2. Two continuous-variable quantum identity authentication schemes are designedby using Gaussian-modulated squeezed states. A newly defined fidelity param-eter parameter is proposed to verify the identity of the communicator and detecteavesdropping. The analytical results show the feasibility and security of thesetwo schemes. By using non-deterministic measurement, the second scheme canresist the attack caused by leak of authentication key, which has a better robust-ness but lower efficiency.3. The security of CVQKD scheme with the imperfect coherent source is investi-gated. The degree of imperfection of coherent source which affects the secu-rity of CVQKD system is bounded. In particular, the noisy coherent source ischaracterized through introducing a party (Fred) who induces the noise with anoptical amplifier. According to the role of Fred, i.e., the untrusted party or neu-tral party, two security bounds to the noise of the coherent source are derived,respectively.4. For bipartite quantum channel, a model of memory quantum channel is con-structed by introducing the memory state, and the quantum capacities of thememory Pauli channels with Markovian correlated noise are derived. In partic-ular, the exact quantum capacities of memory phase flip, bit flip and bit-phaseflip channels and a lower bound of the quantum capacity of memory depolar-izing channel are obtained. The results show that an increase of the degree ofmemory of the channels has a positive effect on the increase of their quantumcapacities. For multi-access transmission channel, a kind of memoryless three-access entanglement preserving channel is proposed, and the purely quantumsuperadditivity of quantum capacity regions of this channel is clarified. More-over, a quantum butterfly network which can achieve quantum network codingis proposed, where the superadditivity also holds.5. We clarify that in some cases, the maximum classical mutual information ob-tained by the two-side measurement will be more suitable than the one-side measurement. And the dynamics of classical and quantum correlations undernondissipative and dissipative decoherences are analytically and numerically in-vestigated with both one-side measures and two-side measures. Specifically, twoqubits under local amplitude damping decoherence and depolarizing decoher-ence channels are considered. We show, under the action of amplitude dampingdecoherence, the quantum entanglement, quantum correlation and nonentangle-ment quantum correlation of different types of initial states with same initialvalues, suffer different types of dynamics. While for the action of depolarizingdecoherence, there does not exist this phenomena. This is very meaningful forthe application of entanglement distribution and quantum cryptography commu-nication.6. The non-Markovian effects of the transmission channel are found and clarifiedto have a positive impact on the increase of secret key rate, thus improve thesecurity of discrete-variable QKD. And the secret key rate may fluctuate nearthe secure point when the coupling strength of the system with the environmentis high enough, thus may incur insecurity of quantum communication betweenthe legitimate parties.7. Two linear optical schemes are designed, which can realize the specific multi-access quantum channel which enables nondestructive two-qubit quantum con-trolled phase operation. The first setup involves triplet Greenberger-Horne-Zeilinger (GHZ) states, which can improve the efficiency1/8of previous pro-posals to1/2. The second proposal involves photon number resolving detectors,which holds the efficiency1/8. And the omission of entangled ancilla input,Bell state measurement and additional complicated single-qubit operations wellreduces the complexity. This can be well implemented in experiment.