Quantum Cryptography, Quantum Networks

HSPSs Boost MDI-QKD Key Rate 60× Over Prior Work

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June 6, 2026 by Ivy Delaney

Institute of Quantum Information and Technology, Nanjing University of Posts and Telecommunications have achieved a secure key rate over 60 times higher than previous measurements in measurement-device-independent quantum key distribution (MDI-QKD) at a 10-dB transmission loss. This increase in data transmission speed results from an efficient MDI-QKD protocol utilizing heralded single-photon sources (HSPSs) that minimize signal degradation, extending the maximum transmission loss beyond 30 dB. The team attained a Hong-Ou-Mandel interference visibility of 95.1% at 10 mW, demonstrating the high quality of the HSPSs and contributing to the improved key rate and transmission distance. The researchers state that this work is expected to play a crucial role in the future development of large-scale quantum communication networks, potentially exceeding 400 km in range with further technological advancements.

Heralded Single-Photon Sources Enhance MDI-QKD Performance

A sixty-fold increase in secure key rate achieved in a recent experiment significantly advances the practicality of measurement-device-independent quantum key distribution (MDI-QKD) systems, even with substantial signal loss during transmission. This improvement allows for secure communication even across channels experiencing up to 10 decibels of transmission loss, a level previously difficult to maintain with acceptable key generation speeds. The team’s success depends on the quality of the HSPSs employed, which exhibited a Hong-Ou-Mandel interference visibility of 95.1% at 10 mW, confirming their ability to generate nearly ideal single photons for quantum communication. This high visibility directly contributes to the enhanced key rate and extends the maximum achievable transmission distance beyond 30 dB, a milestone that pushes the boundaries of secure quantum communication. Chun-Hui Zhang, the contact author at the Institute of Quantum Information and Technology, explained that these improvements are attributed to the efficient protocol used and the high-quality HSPSs prepared in the experiment. Looking ahead, the researchers anticipate further extending the range of their system; with refinements to existing technology, they predict the maximum transmission distance will exceed 400 kilometers.

Recent advances in quantum key distribution (QKD) are pushing the boundaries of secure communication, with researchers from Institute of Quantum Information and Technology, Nanjing University of Posts and Telecommunications now demonstrating transmission distances previously considered unattainable. The experiment successfully extended the maximum transmission loss to over 30 dB, a critical threshold for long-distance quantum cryptography. This achievement significantly expands the potential range of secure quantum key distribution, moving beyond earlier limitations and opening possibilities for exceeding 400 km in future iterations. Maintaining signal integrity at such high loss levels is crucial for practical quantum networks, as it reduces the need for expensive and complex repeater technologies. Researchers believe this work will be instrumental in building large-scale quantum communication networks, and further technological refinements promise even greater distances and key rates, solidifying QKD as a viable solution for safeguarding sensitive data in an increasingly interconnected world.

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MDI-QKD Quantum Communication quantum key distribution Single-Photon Sources
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Ivy Delaney

Ivy Delaney has been working with neural networks and machine learning since the mid-nineties, back when a couple of hidden layers and a long afternoon of training counted as ambitious. She has watched the field go from academic curiosity to the thing quietly running underneath everything, and she brings that long view to quantum computing. For Quantum Zeitgeist she covers the ground where the two fields meet. That means quantum machine learning and the variational algorithms it leans on, and it also means the less glamorous but more interesting story of classical machine learning already doing real work inside quantum machines, decoding error-correcting codes, calibrating noisy hardware and learning the error models that simulators depend on. She writes about the hardware those algorithms have to run on too, and about the post-quantum cryptography scramble that the same hardware has set off. Her stories typically start with the paper, whether that is peer-reviewed work, conference proceedings or an arXiv preprint, with the source linked so you can hold a claim up against the research it came from. She is unimpressed by benchmarks that will not say what they beat, and by demonstrations that only work in the press release.

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