Quantum communication realizes information-theoretic security using photonic quantum states, for example,quantum secure direct communication (QSDC), which can achieve secure and reliable communication in a chan-nel with both noise and eavesdroppers. However, QSDC suffers from large losses and short communication dis-tances, thus being impractical for applications. Here, we have proposed a one-way quasi-QSDC protocol withsingle photons. This protocol enables the simultaneous transmission of information and key exchange using thesame single photons and is robust against loss and error because it uses error correction and spectrum expansiontechniques. In a proof-of- principle demonstration using weak coherent pulses, the system achieved a real-timesecure transmission rate of 2.38 kilobits per second over a 104.8-kilometer standard telecommunication fiber,which set world records in both aspects. This system paved the way for the practical application of QSDC and of-fers a unique method to detect eavesdropping online, which is crucial in certain circumstances.

Paper link: https://www.science.org/doi/epdf/10.1126/sciadv.adt4627