Quantum Key Distribution And Quantum Information Transfer Based On Multiple-path Systems

Cryptography is the most important method to guaranty the security of mil-itary, confidential, bank, company and privacy information transfer. With the de-velopement of internet, digital cash, web bank, the security of information transfer is of increasing importance. Hacker's eavesdropping and the attack of virus, the tool for information warfare, is very dangerous for information security. But, nei-ther the "one-time pad ", a privacy-key craptography which is proved to be secure, nor the two widely used public-key cryptography, the Diffie-Hellman cryptogra-phy and the RSA cryptography, whose security is unproved, meet the demand for application. Especially, the born of Shor's quantum algorithm breaks the secu-rity of the two public-key cryptography absolutely. Classical cryptography can no longer satisfy the increasing demand of information security. On the other hand, quantum cryptography based on the quantum mechanics provides a new way for information security, it is a super tool for cryptography that never occur. So far, various protocols for quantum cryptography have been deeply studied theoretically, and there are also some remakable experiments have been done successfully. Even some primary systems have been presented in the market. However, limited by the current technology, many communities still dedicated to the field. The ultimate goal of this field is to establish a cryptography that can transfer information secure unconditionally over long distances via todays'technology. The exists protocols ,theroretical or experimental, realise information transfer via quantum resource transmitting, one time or many times, through the quantum paths between the legitimate parties. In this paper, we propose some new protocols to realise quan-tum key distribution and quantum information transfer via transmiting quantum resources through the quantum channels(multiple-path) over long distances, and the performance of them are also investigated. The main content of this paper are as follows:In chapter 1, basic knowledge frame of cryptography is introduced, including the main fields of cryptography, the background of qantum cryptography, some well known protocols for quantum cryptography, and the general physical picture of quantum cryptography.In chapter 2, firstly, based on the content of the original BB84 protocol, the security analysis of quantum key distribution is introduced, explicitly, some kinds of attacks and its effects to the performance of QKD systems are presented。Further more, the unconditional security theory of BB84 is introduced. Then, the mode of QKD system that is more applicable, the security theory of many protocols based on this mode are completely introduced.In chapter 3, The pioneering woks of quantum direct communication, another important field of quantum cryptography, are introduced. Then the main contents of this paper axe introduced.In chapter 4, an improved "4+2" one-way two paths protocol for QKD is proposed. QKD via long lossy channel can be realised. A "squash mode" corre-sponding to this protocol ia also presented. Based on this mode, a lower bound of the secure finite key-rate KL is obtained, and the relationship including numerical results between KL and the cricial parameters for this system is derived.In chapter 5, via entangled photon-pair transmitting in a one-way two paths form, a protocol that two-bit intrinsic random number can be distributed between two distant parties is proposed. As the legetimate parties can not determine the result for each QKD round, this protocol is robust when compared with theose prepare measure protocols like the standard BB84 protocol.In chapter 6, first a special discret algorithm is introduced, then a proto-col that can realise quantum secure direct quantum communication (QSDC) by applying the algorithm to quantum bits that will be transmitted through the two-way one path channel between the two distant parties. Own to the algorithm, the eavesdropper Eve can only obtain little informatiom that can be negnect with high probability to be detected. The protocol is secure even compromised in noisy channel.In chapter 7, via a "spin-path" entangled channel, a protocol that can trans-fer the three particle W state and the GHZ state contained arbitary number of particles between two distant parties is proposed. And the effect of white noise of the channel to the information transfer is also investigated.In chapter 8, the conclusion and the future outlook are presented.