Decoy-State Quantum Key Distribution Over a Long-Distance High-Loss Air-Water Channel
Cheng-Qiu Hu, Zeng-Quan Yan, Jun Gao, Zhan-Ming Li, Heng Zhou, Jian-Peng Dou, Xian-Min Jin
Abstract
Atmospheric free space and fiber have been widely exploited as the channels for quantum communication, and have enabled intercontinent and intercity applications. An air-sea free-space channel, being capable of linking the satellite-based quantum resource and underwater vehicle, has now become the last piece of the puzzle in building a global quantum communication network. Here, we present an experimental demonstration of air-water decoy-state quantum key distribution against high loss, meanwhile keeping a low quantum bit error rate less than 2.5% for different distances. We are able to reach a long-distance quantum key distribution in water channel that can enable real-life air-sea quantum-communication tasks. The demonstrated distance, even in coastal water of Jerlov type III, is up to 30 m, about one-order improvement over the proof-in-principle demonstrations in the previous experiments, and the channel loss is equivalent to 345-m-long clean seawater of Jerlov type I, representing a key step forward to practical air-sea secure communication.