QUANTUM SECURE DIRECT COMMUNICATION

Quantum secure direct communication is a quantum communication technology that uses quantum states as carriers to transmit information securely and directly, first proposed by a team at Tsinghua University in 2000. Quantum communication broadly refers to information transfer processing tasks accomplished through the transmission of quantum states, which can be categorized into three types based on the content transmitted: quantum key distribution for transmitting random numbers, quantum secure direct communication for transmitting classical information, and quantum teleportation for transmitting quantum information. After more than two decades of development, quantum secure direct communication has matured and entered practical application: a theoretical framework tailored for scenarios with high loss, high noise, and stringent security requirements has been established; experimental demonstrations of quantum direct communication in optical fibers and free space have been completed; three milestone systems for quantum secure direct communication at the metropolitan, intercity, and network levels have been built; and successful trials have been conducted in various scenarios such as 5G private networks and banking applications. Quantum secure direct communication offers multiple applications: it prevents information leakage by detecting eavesdropping, ensuring information security; identifies exposed locations by monitoring surveillance activities, providing technical support for preventing targeted eliminations and safeguarding commanders' personal safety; and detects intrusion and tampering behaviors, offering novel protection for cybersecurity. Currently, quantum direct communication has been incorporated into relevant planning documents in China, the European Union, and the United States, and is undergoing rapid development. This article briefly outlines the historical development, fundamental principles, research advancements, and future prospects of quantum direct communication.