Perfectly secure quantum communication

A message encoded using a one-time pad cannot be broken. Sending a one-time pad code with perfect privacy has been achieved. A one-time pad message can be sent securely using quantum mechanics and now also send the original message can be sent securely.

Physicists could check quantum states to see if a one time pad message had been overheard. The leakage is detected after it has occurred. An eavesdropper would already have the information by the time physicists found out.

For a one-time pad, a set of random numbers that can be used to encrypt a message. If the one-time pad is overheard, physicists simply disregard it and send another, until they can be sure that the process was completely private.

Getting rid of one-time pads would make sending secure messages far simpler.

The new method uses some initial photons to check for eavesdropping if there is none then the message is sent.

The transmission rate close to security key rates of current commercial quantum key distribution systems.

Quantum secure direct communication (QSDC) is an important quantum communication branch, which realizes the secure information transmission directly without encryption and decryption processes. Recently, two table-top experiments have demonstrated the principle of QSDC. Here, we report the first long-distance QSDC experiment, including the security test, information encoding, fiber transmission and decoding. After the fiber transmission of 0.5 km, quantum state fidelities of the two polarization entangled Bell states are 91% and 88%, respectively, which are used for information coding. We theoretically analyze the performance of the QSDC system based on current optical communication technologies, showing that QSDC over fiber links of several tens kilometers could be expected. It demonstrates the potential of long-distance QSDC and supports its future applications on quantum communication networks.