Enhancing Continuous-variable Quantum-key-distribution with Error-correcting Relays Surpasses Repeaterless Bound
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Long-distance quantum communication secures data using the principles of quantum mechanics, but signal loss limits how far information travels. Swain, Marshman, Dias, and colleagues at the University of Technology Sydney and University of Queensland now demonstrate a significant advance in continuous-variable quantum key distribution, a method for encoding information onto properties of light.
The team combines techniques that amplify quantum signals without introducing extra noise with a method for reducing the impact of random fluctuations, effectively overcoming the limitations of conventional systems. This combined approach allows for secure communication distances exceeding the fundamental rate-distance limit for systems that do not use quantum repeaters, paving the way for more practical and long-range quantum networks.
Relay Station Extends Quantum Communication Range Scientists are developing methods to extend the practical range of continuous-variable quantum-key-distribution (CV-QKD), a secure communication protocol. Current limitations arise from signal loss over long distances, which introduces errors that compromise security.
The team addresses this challenge by proposing and analysing an error-correcting relay station designed to mitigate these losses and improve key rates. This approach strategically positions a relay between the sender and receiver, enabling it to perform quantum error correction on the transmitted quantum states, effectively reducing channel noise and allowing secure key distribution over significantly longer distances. The relay operates by encoding quantum information into continuous variables, such as the amplitude and phase of light, and then correcting errors using a specifically designed protocol. The research demonstrates that the proposed error-correcting relay enhances the performance of CV-QKD systems, achieving a substantial increase in the maximum transmission distance and key rate. Specifically, the relay can extend the secure communication distance by a factor of approximately 3. 5 compared to direct transmission without a relay, maintaining a positive key rate even with substantial channel loss exceeding 10 decibels.
Gaussian States Advance Continuous-Variable QKD This research details theoretical and experimental work in continuous-variable quantum key distribution (CV-QKD) and related quantum communication protocols. CV-QKD encodes information in the amplitude and phase of electromagnetic fields, offering advantages in compatibility with existing telecom infrastructure. The work relies on Gaussian states, fully characterised by their mean and covariance matrix, as the primary resource for CV-QKD, utilising homodyne and heterodyne detection to extract information from received quantum states. The research considers realistic quantum channels with loss, noise, and imperfections. A crucial step in QKD is reconciliation, where raw keys are processed to correct errors and extract a shared secret key, followed by privacy amplification to remove any remaining information an eavesdropper might have. Advancements include quantum scissors, a technique for selecting specific portions of a quantum state to improve the signal-to-noise ratio, and unitary averaging, a method for improving quantum channel performance. Non-deterministic noiseless amplification (NDLA) amplifies quantum signals without adding noise, and is a key component in advanced CV-QKD protocols. Twin-Field QKD (TF-QKD) overcomes the repeaterless bound by using entangled states generated in separate locations, allowing for longer-distance QKD. Quantum teleamplification amplifies quantum signals while preserving their quantum properties, and quantum repeaters extend the range of QKD by overcoming the limitations of lossy channels. The research explores approaches to building quantum repeaters for CV-QKD, demonstrating that techniques like unitary averaging and NDLA can significantly improve channel capacity, allowing for higher key rates and longer distances. CV-QKD is well-suited for integration with existing telecom infrastructure, making it a promising technology for secure communication.
Long Distance Quantum Key Distribution Achieved This research demonstrates a new approach to long-distance continuous-variable quantum key distribution, successfully surpassing the fundamental rate-distance limit for such systems. By combining noiseless linear amplification with unitary averaging, the team achieved robust communication even with significant channel noise and loss. Unitary averaging effectively mitigates the impact of phase noise, while the noiseless amplifier compensates for signal loss, enabling secure communication over extended distances without relying on quantum memories.
The team modelled this system using a beam splitter network to distribute the quantum signal across multiple transmission modes, achieving noise reduction through heralding techniques. While the current work focuses on modelling and demonstrating the principles, the findings offer new insights into practical hybrid quantum communication systems and pave the way for future development of quantum repeater chains. 👉 More information 🗞 Enhancing Long-distance Continuous-variable Quantum-key-distribution with an Error-correcting Relay 🧠ArXiv: https://arxiv.org/abs/2512.11224 Tags: