Chinese scientists have set a world record by achieving twin-field quantum key distribution (QKD) through a 1,002-kilometer optical fiber, marking a critical step toward a future large-scale quantum network.

QKD, a key method in quantum communication, allows two remote users to generate a shared key known only to them, which is used to encrypt and decrypt messages. Its practical application, however, faces a major bottleneck that is distance limit, as a quantum signal can not be amplified and channel transmittance decreases exponentially with distance.

Previously, twin-field QKD was demonstrated in lab settings through spooled fiber of up to 830 kilometers.

In a study published in the journal Physical Review Letters, scientists from institutions such as the University of Science and Technology of China, the Jinan Institute of Quantum Technology, the Shanghai Institute of Microsystem and Information Technology said that the longest distribution distance reached was 1,002 kilometers with a secure key rate of 0.0034 bits per second.

During their experiments, the scientists developed dual-band phase estimation and ultra-low noise superconducting nanowire single-photon detectors to suppress system noise, which impedes the production of secure keys in the long distance.

The study has verified the feasibility of twin-field QKD at a very long distance, and shed light on its prospects in long-haul quantum communication, according to the University of Science and Technology of China.