An efficient quantum secure direct communication scheme with authentication

In this paper an efficient quantum secure direct communication (QSDC) scheme withauthentication is presented, which is based on quantum entanglement andpolarized single photons. The present protocol uses Einstein--Podolsky--Rosen (EPR) pairs and polarizedsingle photons in batches. A particle of the EPR pairs is retainedin the sender's station, and the other is transmitted forth and backbetween the sender and the receiver, similar to the `ping--pong'QSDC protocol. According to the shared information beforehand, thesetwo kinds of quantum states are mixed and then transmitted via aquantum channel. The EPR pairs are used to transmit secret messagesand the polarized single photons used for authentication andeavesdropping check. Consequently, because of the dual contributionsof the polarized single photons, no classical information is needed.The intrinsic efficiency and total efficiency are both 1 in thisscheme as almost all of the instances are useful and each EPR paircan be used to carry two bits of information.