The world has broken through the quantum key limit for the first time

The world has broken through the quantum key limit for the first time. The key rate of the true single-photon source has soared by 79%.

Quantum Key Distribution (QKD) is an encryption technology based on quantum physical principles and shows great potential in enhancing communication security. This technology transmits encryption keys by using the quantum states of photons or other particles. Since these quantum states cannot be replicated or measured without changing their states, it greatly increases the difficulty for malicious parties to intercept the communication content between the two sides without being detected. Due to the difficulty in preparing true single-photon sources (SPS), most of the quantum key distribution (QKD) systems currently developed rely on attenuated light sources that simulate single photons, such as low-intensity laser pulses. Since these laser pulses may also contain no photons or multiple photons, only about 37% of the pulses used in the system can be used to generate security keys. Chinese researchers have recently successfully overcome the limitations of the previously proposed quantum Key distribution (QKD) system. They have utilized genuine single-photon sources (SPS, that is, systems capable of emitting individual photons on demand).

The main goal of the researchers is to build a physical system capable of emitting high-brightness single photons on demand, thereby overcoming the fundamental limitations faced by the weakened light sources used in the past to construct quantum key distribution (QKD) systems. Their hope is that this system can enhance the reliability and performance of quantum key distribution (QKD) technology, thereby laying the foundation for its future deployment in real-world environments. At present, the experiment has achieved very promising results because their SPS has been found to have extremely high efficiency and significantly increase the rate at which the QKD system generates security keys. Overall, these findings highlight the potential of SPS-based QKD systems, indicating that their performance can significantly surpass that of WCP-based QKD systems. “We have demonstrated for the first time that the performance of QKD based on SPS exceeds the fundamental rate limit of WCP,” the researchers said. In the field QKD test of the free-space urban channel with a loss of 14.6(1.1) dB, we achieved a secure key rate (SKR) of 1.08 × 10−3 bits per pulse, which was 79% higher than the actual limit of the QKD system based on weakly coherent light. However, at present, the maximum channel loss of the SPS-QKD system is still lower than that of the WCP-QKD system. The lower channel loss observed by the researchers in their quantum key distribution (QKD) system did not stem from the system itself, but was attributed to the residual multi-photon effect in the decoy-free protocol they were running. As part of future research, they hope to enhance the loss tolerance of the system by further optimizing the performance of the single-photon source (SPS) at the bottom layer of the system or introducing bait states into the system. It is believed that continuous technological progress will gradually promote the development of quantum key distribution (QKD) towards practical and general applications.