Frequency-matching Quantum Key Distribution Achieves Secure Communication over 296.8km Fibre with Compensated Laser Frequency Offsets
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Quantum key distribution promises secure communication by fundamentally protecting information from eavesdropping, but practical implementation faces challenges from instability in the light signals used. Hao-Tao Zhu, Yizhi Huang, and Abdullah Rasmita, alongside Chao Ding, Xiangbin Cai, and Haoran Zhang, address a key issue, the disruption caused by slight differences in the frequency of the lasers used in these systems.
The team demonstrates a new method employing a simple photodiode to actively compensate for these frequency differences, effectively stabilising the quantum signals. This innovation allows them to achieve exceptionally low error rates in a long-distance fibre optic link, exceeding previous performance limits over a distance of 296. 8km and paving the way for more robust and practical quantum communication networks. Common-Clock Phase Stabilisation for Quantum Key Distribution Quantum key distribution (QKD) enables information-theoretically secure communication, protecting data from eavesdropping. Maintaining stable phases within QKD systems presents a significant challenge, particularly in advanced schemes. The primary source of phase instability arises from slight differences in the frequencies of the lasers used. Researchers have developed a method to synchronize these lasers using a common-clock reference, eliminating frequency offsets and dramatically reducing phase fluctuations. This involves establishing a bidirectional optical link, allowing for continuous phase monitoring and active feedback control. The system utilizes a frequency comb to distribute a stable clock signal to both lasers via the optical link. Real-time phase measurements then drive adjustments to each laser’s frequency, maintaining a constant phase difference and stabilizing the entire system. Extensive simulations and experimental validation confirm that this method substantially reduces phase fluctuations and improves QKD system performance. Mode-Pairing QKD Extends Secure Distance Traditional quantum key distribution (QKD) systems face a trade-off between key generation rate and communication distance. Overcoming this limitation requires innovative approaches that avoid trusted repeaters, which introduce security vulnerabilities. Researchers have demonstrated mode-pairing QKD, a novel technique that uses interference between different spatial modes of photons to overcome this rate-distance limit, creating entanglement between photons in different modes. Experiments have shown that mode-pairing QKD surpasses the rate-distance limit of traditional QKD systems, paving the way for long-distance secure communication. The implementation utilizes Sagnac interferometers to stabilize interference, alongside precise polarization control and sensitive single-photon detectors. Field tests over real-world fiber optic networks demonstrate the feasibility of deploying these technologies in practical scenarios. Further refinements, such as post-measurement pairing, enhance the security and stability of the system.
Frequency Compensation Boosts Quantum Key Distribution Researchers have developed a method to improve the stability of quantum key distribution systems, addressing a significant challenge caused by discrepancies between the frequencies of the lasers used. This new technique employs a classical photodiode to actively compensate for these frequency differences, ensuring more reliable communication. Implementing this approach within a mode-pairing system, the team achieved an error rate approaching the theoretical limit over a fiber optic cable spanning 296. 8 kilometers, exceeding previously established limits on key generation rates. This advancement simplifies the requirements for building practical quantum communication systems by removing the need for complex and expensive components. The method’s compatibility with existing classical communication channels and potential for extending communication distances through the incorporation of optical amplifiers further enhances its feasibility for real-world deployment, including integration into satellite-ground links and expansion through wavelength multiplexing. This work provides a strong foundation for building scalable and efficient quantum networks. 👉 More information 🗞 Frequency-matching quantum key distribution 🧠 ArXiv: https://arxiv.org/abs/2512.05496 Tags: Rohail T. As a quantum scientist exploring the frontiers of physics and technology. My work focuses on uncovering how quantum mechanics, computing, and emerging technologies are transforming our understanding of reality. I share research-driven insights that make complex ideas in quantum science clear, engaging, and relevant to the modern world. Latest Posts by Rohail T.: Noma-cvqkd System Achieves 23% Higher Secret Key Rate with 0.1 Precision under Quantum Attacks December 10, 2025 Bohmian Trajectories Within Hilbert Space Quantum Mechanics Resolve the Measurement Problem Using a Stochastic Process December 10, 2025 Quantum Geometry Defines, And, Wave Magnet Properties, Enabling Analysis of Anomalous Hall Conductivity December 10, 2025