China University of Science and Technology realizes device-independent quantum key distribution

Pan Jianwei and his colleagues Zhang Qiang and Xu Feihu from the University of Science and Technology of China have experimentally demonstrated the rationale of device-independent quantum key distribution (DI-QKD) internationally for the first time by developing a device-independent theoretical protocol and constructing an efficient optical quantum entanglement system. The findings were published online July 28 in Physical Review Letters as Editors' Suggestion, It has been reported on the American Physical Society (APS) website Physics under the title "Hiding Secrets Using Quantum Entanglement".

Quantum key distribution (QKD), compared with traditional communication protocols, enables two remote users to share the key of information theory security. Combined with the encryption method, it can ensure the unconditional security of communication in principle. Traditional QKD schemes usually require a certain understanding and trust of the equipment used, but in real conditions, the equipment may have some imperfect characteristics. These features often provide side channels for attackers to threaten system security, resulting in potential security risks under realistic conditions. The main solution is to test the equipment and develop the relevant standards to ensure its safety under realistic conditions [Rev. Mod.Phys.92, 025002 (2020)].

Device-independent quantum key Distribution (DI-QKD) provides a new secure coding scheme that does not depend on the specific functions and characteristics of the device, based on the basic test of non-vulnerability quantum mechanics. Based on this protocol, the security of QKD can be guaranteed through the violation of Bell inequality without any calibration of the equipment, which has been highly valued and widely concerned by the academic circles at home and abroad. However, the implementation of DI-QKD is very difficult, for example, 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.

FIG. 1 Device independent quantum key distribution experimental setup

In order to achieve this goal, Pan Jianwei's team conducted theoretical and experimental research. In theory, they proposed an original stochastic post-selection DI-QKD theoretical scheme [Phys. Rev. Lett. 128, 110506 (2022)]. The core idea is to increase the system's tolerance for loss effectively by randomly adding noise to the experimental measurement results and removing the results that contain a small amount of correlation information but have large errors, so as to make it possible to realize DI-QKD under the state of the art. In terms of experiments, they used the principle of spontaneous parametric downconversion to build an efficient optical entanglement source by optimizing the parameters of the space optical path, and combined with the single photon detector of efficiency rate, the system efficiency reached 87.5%, surpassing all previous reported optical experiments. At the same time, by adjusting the placement Angle of the nonlinear crystal to limit its reflection of parametric light, the quantum state fidelity generated in the experiment reaches 99.5%, which meets the requirements of the theoretical scheme for the system performance. On this basis, Pan Jianwei's team achieved the first demonstration of the principle of DI-QKD based on an all-optical system, with a code rate of 466 bps, and verified that the system can still generate secure quantum keys when the fiber length reaches 220m.

This is Pan Jianwei's team's work on device-independent quantum information processing, Following the fundamental test of device-independent quantum mechanics [Phys. Rev. Lett. 118, 140402 (2017), Phys. Rev. Lett. 121, 080404 (2018)] and device-independent quantum random number generation [Nature 562, 548 (2018), Nature Physics 17, 448 (2021)]. This work is of great significance for revealing the deep connection between the fundamental test of quantum mechanics and quantum information processing, developing secure key distribution, and constructing future quantum networks.

At the same time, two other related work by international peers based on ions and atoms was also published recently in the journal Nature, which is an important step towards the widespread application of quantum communication with device-independent security in the future.

Doctoral students Wenzhao Liu and Yuzhe Zhang are co-first authors of the experimental paper. The work was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology, Shanghai Municipality and Anhui Province.

Article link：https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.050502

APS Physics website link：https://physics.aps.org/articles/v15/116

(Hefei National Research Center for Microscale Matter Science, Quantum Innovation Institute, Scientific Research Department, Chinese Academy of Sciences)
Source: HKUST News Network