Quantum secure direct communication

Quantum communication exploits the principles of quantum mechanics in the transmision and processing of information. It has the advantages of high security and high capacity. Quantum secure direct communication (QSDC) is a new mode of quantum coomunication by Long and Liu in which secret information can be transmitted securely and directly over quantum channels. Since it was first proposed in 2000, QSDC has been developed very fast. In this review, we will explain the basic principles of QSDC and describe some typical QSDC protocols. Toward the end of the review, we will introduce the new trends in the QSDC research and give a perspectiv of QSDC research.