For the first time, scientists have implemented device-independent quantum key distribution

Academician Pan Jianwei of the University of Science and Technology of China and his colleagues Zhang Qiang and Xu Feihu have achieved the principle demonstration of device-independent quantum key distribution (DI-QKD) for the first time in the world through the development of device-independent theoretical protocols and the construction of high-efficiency optical quantum entanglement systems. The results of the research were published online in the form of editors’ recommendations in the Physical Review Letters.

Device-independent quantum key distribution experimental device .png

Device-independent quantum key distribution experimental device Courtesy of the University of Science and Technology of China

Compared with traditional communication protocols, quantum key distribution (QKD) enables two long-distance users to share information theory security keys, combined with one-at-a-time encryption, to ensure unconditionally secure communication in principle. Traditional QKD solutions usually require some understanding and trust in the device used, but under real-world conditions, the device may have some imperfect characteristics. These features often provide attackers with a side-channel that threatens system security, creating potential security risks under real-world conditions. The main solution today is to test the equipment and develop the relevant standards to ensure its safety under real-world conditions.

Device-Independent Quantum Key Distribution (DI-QKD) provides a new set of secure coding solutions that do not depend on the specific functions and characteristics of the device, based on the vulnerability-free fundamentals of quantum mechanics. Based on this protocol, no calibration of the device is required and the real-world security of QKD can be guaranteed. However, the implementation of DI-QKD is very difficult, such as in optical systems, most of the existing theories give no less than 90% of the system detection efficiency requirements, far beyond the existing technical level.

In order to achieve this goal, Pan Jianwei’s team conducted exploration and research from both theoretical and experimental aspects. Theoretically, the team proposed an original random post-selection DI-QKD theoretical scheme. The core idea is to effectively improve the system’s tolerance for loss by randomly adding noise to the experimental measurement results and eliminating the results that contain a small amount of correlated information but have large errors, making the implementation of DI-QKD possible at the existing technical level.

In terms of experiments, the team used the principle of spontaneous parameter downconversion to build a high-efficiency optical entanglement source by optimizing the parameters of the spatial optical path, and combined with a high-efficiency single-photon detector, the system efficiency reached 87.5%, exceeding all previous reported optical experiments. At the same time, the fidelity of the quantum state generated in the experiment reaches 99.5%, which meets the requirements of the theoretical scheme for system performance.

On this basis, Pan Jianwei’s team for the first time realized the DI-QKD principle demonstration based on the all-optical system, with a bit rate of 466bps, and verified that the system can still generate a secure quantum key when the fiber length reaches 220m.

It is reported that this is another important progress of Pan Jianwei’s team in the processing of device-independent quantum information, following the basic test of device-independent quantum mechanics and the generation of device-independent quantum random numbers. This work is of great significance for revealing the deep connection between the fundamental tests of quantum mechanics and the processing of quantum information, developing secure key distribution, and building future quantum networks. (Source: China Science Daily Wang Min)

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