Improved Quantum “Ping-Pong” Protocol Based on Five-Qubit GHZ State and Classical CNOT Operation

Abstract

To enhance the efficiency of eavesdropping detection in the “Ping-Pong” protocol, an improved “Ping-Pong” protocol based on five-qubit GHZ state and classical CNOT operation is presented. The five-qubit GHZ state is used to detect eavesdroppers, and the classical CNOT operation served as one-time-pad is used to ensure the security of the protocol. In the security analysis, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information eavesdroppers can obtain and the interference introduced. If the eavesdropper obtains the same amount of information, she must face a larger detection probability in the proposed scheme than the other two, and if obtains all the information, the detection rate of the original Ping-Pong protocol is 50%; the second protocol which used two particles of EPR pair as detection particles is also 50%; while the presented protocol is 92%. At last, the security of the proposed protocol is discussed. The analysis results indicate that the protocol in this paper is more secure than the other two.