In the realm of long-distance quantum communication, asynchronous measurement-device-independent quantum key distribution (AMDI-QKD) stands out for its experimental simplicity and high key rate generation. Despite these advantages, there exists a challenge in finding a balance between simplifying the laser system further and achieving high key rates. To address this challenge, we have devised a postmeasurement compensation scheme to accurately estimate the mutual frequency offset between two compact lasers using just the announced quantum-signal detection results, thereby obviating the need for optical reference light. As a result, we demonstrate an AMDI-QKD system operating at 2.5 GHz and achieving secure key rates (SKRs) of 537 and $\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">101</span>}\text{<span style="background-color: rgb(255, 255, 255); font-family: 微软雅黑, "Microsoft YaHei"; font-size: 16px;">?</span>}\text{<span style="background-color: rgb(255, 255, 255); font-family: 微软雅黑, "Microsoft YaHei"; font-size: 16px;">?</span>}\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">kbit</span>}<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">/</span>\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">s</span>}$ at distances of 100 and 201 km, respectively, showcasing a significant key rate improvement compared to similar setups. By leveraging ultrastable lasers, we achieve the highest SKRs with measurement-device-independent security within the 100–400-km range. Over 100 km, we reach a remarkable key rate of $\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">1.03</span>}\text{<span style="background-color: rgb(255, 255, 255); font-family: 微软雅黑, "Microsoft YaHei"; font-size: 16px;">?</span>}\text{<span style="background-color: rgb(255, 255, 255); font-family: 微软雅黑, "Microsoft YaHei"; font-size: 16px;">?</span>}\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">Mbit</span>}<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">/</span>\mathrm{<span\; style="background-color:\; rgb(255,\; 255,\; 255);\; font-family:\; 微软雅黑,\; "Microsoft\; YaHei";\; font-size:\; 16px;">s</span>}$, which could enable real-time one-time-pad video encryption. These findings render AMDI-QKD as a promising contender for the establishment of high performance and cost-effective large-scale intercity quantum networks.

Paper link: https://journals.aps.org/prx/abstract/10.1103/PhysRevX.15.021066