Compared with optical quantum communication, classical communication cannot be compared with it in security and efficiency. Security-Quantum communication will never "leak". The key of quantum encryption is random. Even if it is intercepted by a thief, the correct key cannot be obtained, so the information cannot be cracked. Secondly, if the quantum state of one particle changes, the quantum state of another particle will also change immediately. According to quantum theory, any macroscopic observation and interference will immediately change the quantum state and make it collapse, so the information obtained by the thief due to interference has been destroyed, not the original information. Efficient, transmitted unknown quantum States will be entangled before being measured, that is, they represent multiple States at the same time. For example, one quantum state can represent two numbers: 0 and 1, and seven such quantum states can represent 128 states or 128 numbers: 0~ 127. The transmission of optical quantum communication is equivalent to 128 times that of classical communication. As you can imagine, if the transmission bandwidth is 64 bits or higher, the difference in efficiency will be staggering 2 and higher. Quantum communication has absolute security characteristics that traditional communication methods do not have. It not only has great application value and prospect in the fields of national security, finance and other information security, but also gradually enters people's daily life. In order to make quantum communication from theory to reality, scientists at home and abroad have done a lot of research work since 1990s. Since 1993, researchers from IBM in the United States put forward the theory of quantum communication, both the National Science Foundation and the Defense Advanced Research Projects Agency have conducted in-depth research on this project. 1999, the European union concentrated international efforts on quantum communication, with as many as 12 research projects, and the Japanese Ministry of Posts and Telecommunications regarded quantum communication as a strategic project in 2 1 century. China has been engaged in the research of quantum optics since 1980s. In recent years, the Quantum Research Group of China University of Science and Technology has made outstanding achievements in quantum communication.