Deterministic Quantum Secure Direct Communication Protocol Based on Hyper-Entangled State.

A quantum secure direct communication (QSDC) protocol based on the hyper-entangled state is proposed to improve the efficiency of eavesdropping detection in an improved "ping-pong" protocol, in which we use the hyper-entangled state to detect eavesdropping during the quantum communication. In the security analysis, we use the entropy theory method to calculate the amount of information and compare the detection strategy of two QSDC protocols quantitatively by comparing the constraint between the maximal amount of information that the eavesdropper can get, and the probability that the eavesdropper is detected. The probability of being detected will be 50% in the original QSDC protocol which based on the Bell states if the eavesdropper attempts to get all the information, however, in the proposed protocol this probability can reach 75%, which indicates that the proposed protocol is more secure.