Back in the 1980s, quantum physicists discovered that the strange rules of quantum mechanics allowed information to be sent from one part of the universe to another with complete privacy.
Within a few years, researchers demonstrated the technique in the lab, and today quantum cryptography is becoming commercially viable thanks to companies such as ID Quantique in Geneva, Switzerland.
The private message is not sent using quantum mechanics at all. If it’s possible to send the one-time pad securely using quantum mechanics, why not just send the original message that way? The new process is called quantum secure direct communication, and the Chinese team have used it through 500 meters of fiber-optic cable for the first time. Physicists can check this because quantum particles cannot be measured without destroying the information they contain.
The method exploits the quantum phenomenon of entanglement.