The Research Of Obtainable Mutual Information By Multiple Quantum Measurements

In the information age, people want to find a better and faster way to obtain and transmit information. People apply the knowledge of quantum mechanics to the information science, and produce Quantum Information science. The practical application value and the major scientific significance cause all aspects of social research it. Thus, the new information age is coming. One of the important parts is the Quantum Cryptography, compared with the classic secure communication, in principle,we can not decipher and eavesdrop communicate.So it is absolutely safe. But in quantum information process, we inevitably will be affected by some environmental impact outside. These disturbances can reduce or hinder to get original information of transfer. In order to overcome these disadvantages, people try to find ways to improve the amount of information extraction or resist external interference.This paper studies about the method by information transmitter controls the informational extraction to extract information, and discuss some possible applica-tion in the information transfer. We assume that the transmitter,Alice,makes the information coded in binary codes into two nonorthogonal states,|ψ>1,|ψ>2, and (ψ1|ψ2)=cos 2α, The probability of the two states are P1, P2 correspondingly, and P1+P2=1.Then Alice randomly chooses a state from two nonorthogonal states and sends to Bob who is the first measurer.Bob measures it and gets the informa-tion. Generally the communication is over after Bob’s measurement, but now there is another measurer, Charlie, who doesn’t directly communicate with Alice, he can still extract information from the reduced states after Bob’s measurement. Now the information of Alice’s can be extracted one by one. What the factors of ex-tracting information by Bob and Charlie? We find the the two parameters P and a of Alice influence the information to be extracted by information extractors. Then we consider and calculate the maximum probability of Bob and Charlie’measure when Alice’s two non-orthogonal states P1= P2 or P1≠ P2 in both cases are sent to Bob. We apply the concept of the quantum mutual information to describe the amount of information that they extract, then calculate the the quantum mutual information of Alice and Bob, Alice and Charlie correspondingly. We find Alice can control the parameters P and a to assign the information between Bob and Charlie. Specially Alice can make the quantum mutual information of Alice and Charlie is zero. This discovery can be applied in detect the attack, so we discuss the possible application about the filed of them. By controlling the parameters P and a of Alice distribute the information to be extracted not only can promote the increase of information diversity, but also prove the information security. This result is very meaningful.