Keywords: 
• 量子隐形传态通信 /
• 全用型量子密钥分发 /
• 确定性量子密钥分发 /
• 量子安全直接通信

Abstract: Quantum communication protects information security by means of the basic laws of quantum mechanics and has aroused the wide public interest over the recent years. Quantum communication consists of quantum key distribution, quantum secure direct communication, quantum teleportation, quantum dense coding, and quantum secret sharing. The purpose of quantum key distribution, quantum secure direct communication and quantum secret sharing is to protect the security of information and thus they are called quantum cryptography. In quantum key distribution and secret sharing, data transmitted in the quantum channel are random keys rather than information, and the information is sent through another classical communication. The direct communication of information through quantum channel is realized in quantum secure direct communication. In this paper, we present a protocol for quantum communication by using quantum teleportation (QCUQT), and analyze it in detail. First, we answer the question whether QCUQT is a type of quantum secure direct communication. In QCUQT, only computational basis states are teleported, and both the Bell-basis measurement and the single particle operations can be simplified. It is found that the QCUQT is equivalent to the combined process of a quantum key distribution plus a classical communication rather than a type of quantum secure direct communication. In order to read out the information in the quantum channel, classical communication is required by QCUQT. Some misunderstandings about QCUQT are discussed and clarified in the paper. It was mistaken that the transmission of quantum state in QCUQT is irrelevant to the channel noise nor the distance between two parties, and QCUQT can even be used to realize superluminal communication. Our study shows that the QCUQT is affected by the medium and also the distance between two parties, and it does not have an advantage over quantum key distribution, and cannot realize quantum superluminal communication either. We also compare the QCUQT with quantum key distribution, quantum secure direct communication, and classical one-time-pad in several aspects such as the nature of the data in quantum channel, the way of reading out the key, the way of transmitting messages, andthe amount of data carried in the process. We also point out the characteristics of each type of communication. It is concluded that single-photon quantum key distribution is easier to realize than QCUQT because single-photon detection and generation are easier to realize than the Bell-basis measurement and generation of EPR pairs. In particular, we discuss the use of these protocols in space communication and it is suggested that quantum secure direct communication be a better choice in outer-space quantum communication because of the low loss in quantum channels there.