Secure Quantum Dense Coding Via Non-maximally Entangled State And Its Realization In Cavity QED

Quantum information theory is a rising interdisciplinary field whichcombines classical communication and quantum mechanics. QuantumInformation from the birth to the rapid development shows a very broadapplication prospects. It includes quantum communication and quantumcalculates. In quantum information theory, the most important resource isentangled states. Because of its non-locality, it can be used in manyregions, especially in quantum communication. Such as quantum densecoding (QDC), quantum teleportation, quantum secret sharing(QSS) andquantum cryptography, etc. QDC is one of the important applications ofquantum entanglement in quantum communication, which can transmittwo bits of classical information by sending only one quantum bit. So itdemonstrated strong growth prospects. In recently years, QDC has beenprogressed both in theory and experiment.In chapterâ… , we briefly review the history and researching actualityof quantum information theory, and the importance of quantumentanglement in quantum information. Some basic theories of quantumentanglement are introduced, including definition of entangled states andclassification, several mainly measurements of entanglement degree,simple application, several kinds of entangled states and two manners ofstate's measurement.In chapterâ…¡, the basic concept of quantum dense coding are induced,as well as the quantum dense coding of the latest developments. Then we present a secure scheme for probabilistically implementing a quantumdense coding via tripartite non-maximally entangled GHZ-like state andits realization in cavity QED. The scheme employs the idea of quantumsecret sharing and makes the transmitted information shared by tworeceivers. By collaboration, both of the two receivers could extract thesender's information. It has the merit of more secure. We usenon-maximally entangled GHZ-like state as the quantum channel. So thesuccessful probability doesn't equal to 1. It equals to the two times ofmodular square of smaller coefficient in the given GHZ-like state.In chapterâ…¢, we focus on the influence to the quantum dense codingwhen noisy exists. Here quantum noisy is described by phase damp. Weanalyzed the impact on the probabilistic QDC when the phase dampexists. In this case, the receiver can't know the message which is send bythe sender in a deterministic way. We can only calculate the successfulprobability which is s=1-Q~2q~2(1-q~2). It has something to do with theinitial state's parameter Q q, but has nothing to do with the decaycoefficient f. However, this time the probability of success will includeany error. We can use probability of mistakes to describe it. Theprobability of error is f=1/2Q~2[1-(1-p)~2(|q|~2+q~2)+q~2|q|~2]. And thesuccessful probability s will become bigger when the decay coefficient fbecomes bigger.In chapterâ…£, it is summary and outlook.