Study On Continuous Variable Quantum Dialogue Protocols Based On Two-mode Squeezed States And GHZ States

With the increasing computing ability of classical computers and the constantly deeper researches on quantum computer, the security of classical cryptography will face a growing threat. Quantum cryptography is based on classical cryptography and quantum informatics, and its unconditional security is usually guaranteed by the non-cloning theorem and the uncertainty principle, which allows quantum cryptography to perform better with potential applications. Among the quantum information science, quantum secure direct communication(QSDC) is one of the most promising applications, where secret information could be directly transmitted to receiver via a quantum channel. In 2002, Beige et al. proposed the QSDC protocol,since then various QSDC strategies based on different entangled states have been proposed.Quantum dialogue(QD) is a kind of protocol, which permits two communication parties to achieve the goal of sending and receiving information within the same time, and it also can be called as the two-way QSDC protocol. In the QD protocol, two communication parties can mutually exchange secret information simultaneously via a quantum channel. Since the first QD protocol was proposed by Nguyen BA in 2004, it has been attracting much attention. Unfortunately, the proposed discrete variable quantum dialogue protocols are difficult to realize or suffer from lower transmission efficiency. In contrast, the continuous-variable quantum communication can be realized by optical devices easily. In recent years,continuous-variable quantum communication has been attracting a lot of attention both in theoretical and experimental aspects. By focusing on the hot subject of continuous-variable quantum dialogue(CVQD), exploiting continuous variable GHZ entangled states, the quantum dense coding and the pattern of block transmission,three novel continuous variable quantum dialogue protocols are proposed. Moreover,combining the theory of quantum cryptography, the security and the efficiency of these three proposed QD protocol are analyzed, the main research achievements can be described as:A continuous-variable quantum dialogue protocol is designed by using two-mode squeezed vacuum states. The two communication parties encode their own secret information into the entangled optical modes with the translation operations.Each communication party can deduce their counterparts' secret information with the help of his or her secret information and the Bell-basis measurement results. The security of the protocol is guaranteed by the correlation between two-mode squeezed vacuum states and randomly selected time slots to perform decoy states translation operations. Compared with the discrete variable quantum dialogue protocols, the proposed protocol is easy to realize with perfect utilization of quantum bits.With qubit block transmission strategy, a novel multiparty controlled quantum dialogue protocol with continuous-variable states is devised. During the multiparty controlled QD protocol, the secret information would be encoded into optical modes with translation operation, and the secret information of each counterpart can be recovered only if all the controllers permit this term of communication. Security analysis shows that the multiparty controlled QD protocol is free from information leakage and the man in the middle attack.A novel three-party quantum dialogue protocol is proposed based on continuous-variable GHZ states, in which any one of the three-party can deduce the encoding operations the other two parties, combining the encoding rule, he(she) could obtain the secret information of the counterpart with higher efficiency. The security of the three-party QD protocol is guaranteed by the GHZ entangled states and decoy states translation operations within random time slots. Moreover, if employing n-particle continuous-variable GHZ states, the three-party QD protocol can be easily generalized to N-party QD protocol.