A new record! China’s scientific research team has realized 508 kilometers of optical fiber quantum communication

China Science News learned from the Beijing Institute of Quantum Information Science that the team of Yuan Zhiliang, chief scientist of the academy, cooperated with Yin Hualei, associate professor of Nanjing University, and others to achieve the first experimental asynchronous measurement device-independent quantum key distribution that breaks the security code rate-distance boundary, successfully realized 508 kilometers of optical fiber quantum communication, as well as record-breaking intercity key rate and two-photon interference distance. On June 20, the relevant research results were published in Physical Review Letters.

It is understood that the key rate of point-to-point quantum key distribution (QKD) decays linearly with the loss of the channel. Dual-field quantum key distribution (TF-QKD) has attracted much attention and success because the key rate can be linearly down by the square root of channel attenuation. However, the implementation of the two-field protocol system is complex, and modules such as phase tracking and frequency calibration are usually required to ensure stable long-distance single-photon interference.

In 2022, Yin Hualei et al. proposed a novel asynchronous measurement device-independent quantum key distribution (Asynchronous MDI-QKD) protocol, which realizes time multiplexing through classical post-processing, constructs two-photon Bell states, and establishes a bridge between MDI-QKD and TF-QKD. The post-measurement pairing technology can greatly reduce the strict requirements for laser source and phase stability in the TF-QKD system, and achieve higher security key rates in medium and long distances.

Comparison diagram of synchronous and asynchronous pairing scheme Courtesy of Beijing Institute of Quantum Information Science

Based on the asynchronous measurement device-independent quantum key distribution protocol and a new response filtering method, Yuan Zhiliang’s team developed a quantum key distribution system that can still perform stable asynchronous two-photon interference within a 200 microsecond time interval, breaking through the security code rate boundary for the first time without phase tracking technology and strict combined security limited key analysis.

Yuan Zhiliang introduced that the experimental work achieved a record two-photon interference distance and intercity key rate, increasing the maximum optical fiber transmission distance of MDI-QKD from 404 km to 508 km. At 400 km, its key rate is increased by 6 orders of magnitude compared with before, and the security key rate at 201 km and 306 km exceeds 57,000 bits per second and 5,000 bit/s respectively, which can meet the real-time encryption needs of voice communication. The research results are of great significance for commercialization, high-security intercity quantum key distribution system and the construction of cost-effective intercity quantum security network in China. (Source: Shen Chunlei, China Science News)

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