China University of Science and Technology Achieves 100 Gigabit Rate Quantum Key Distribution

Academician Pan Jianwei and Professor Xu Feihu of the University of Science and Technology of China cooperated with researchers from the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences, the Jinan Institute of Quantum Technology, Harbin Institute of Technology and other units to achieve real-time quantum key distribution at 100 megabit rates internationally by developing key technologies such as high-fidelity integrated photonics quantum state regulation and high-count rate superconducting single-photon detection, and the experimental results improved the previous code rate record by an order of magnitude. On March 14, the results were published online in the internationally renowned academic journal Nature Photonics.

High code rate quantum key distribution device diagram Photo courtesy of China University of Science and Technology

Quantum Key Distribution (QKD) is based on the fundamental principles of quantum mechanics and enables unconditionally secure and confidential communication in principle. Improving the code rate of QKD plays a crucial role in its practical use. The high bitrate can provide services for more users and realize applications with high bandwidth requirements, such as big data sharing and distributed storage encryption. Previously, the highest real-time bitrate in the world was 10 Mb/s (under 10 km standard fiber channel). In order to achieve higher key rates, technical bottlenecks such as the sender, receiver, and post-processing of the system need to be addressed. At the sending end, high-bit-rate QKD requires high-fidelity quantum state modulation, but the existing QKD system produces a high bit error rate under high-speed modulation. At the receiving end, single-photon detectors with both high efficiency and high count rate capabilities are indispensable, and superconducting nanowire single photon detectors (SNSPDs) have the advantages of high efficiency and low noise, but their count rates are usually limited by long recovery times.

The research group of Pan Jianwei and Xu Feihu has developed a high-speed high-fidelity polarization state modulation technology on integrated photonic chips, with a system repetition of 2.5 GHz and a qubit bit error rate better than 0.35%. Combined with the latest eight-pixel SNSPD developed by the team of You Lixing of the Shanghai Institute of Microsystems of the Chinese Academy of Sciences, it realizes single-photon detection with high counting rate and high efficiency, and can still maintain 62% detection efficiency when 550 million photons per second are input. At the same time, the research group developed polarization feedback control and high-speed post-processing modules.

On the basis of the above technological breakthroughs, the research team achieved a key rate of 115.8 megabits per second under a standard fiber channel of 10 km, an order of magnitude higher than the previous record; the system operated stably for more than 50 hours, and the bitrate exceeded 200 bits per second at a transmission distance of 328 km.

The research results show that QKD can achieve real-time key distribution at 100 megabit rates, which meets the requirements of high-bandwidth communication, which is of great significance for the large-scale practical application of quantum communication in the future. (Source: Wang Min, China Science News)

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