Random Coding Advances Continuous-Variable QKD for Long-Range, Secure Communication
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Quantum Key Distribution (QKD) offers a fundamentally secure method for exchanging cryptographic keys, bypassing the computational assumptions that underpin classical cryptography, and researchers continually seek to extend its range and practicality.
Arpan Akash Ray from Eindhoven University of Technology, along with Boris Skoric, present a new approach to error correction within continuous-variable QKD systems, which utilise the properties of light rather than individual photons. Their work addresses a significant challenge in long-distance QKD, namely the difficulty of correcting errors when signals become extremely weak, and introduces a random-codebook method that is well-suited to real-time implementation.
The team demonstrates that this method achieves a key generation rate exceeding existing techniques, potentially enabling secure communication over significantly longer distances and paving the way for more robust quantum networks. Magnetic field. Implementing this correction in real-time presents a significant challenge.
This research introduces a random-codebook error correction method specifically designed for long-range Gaussian-modulated CVQKD. The method employs likelihood ratio scoring with block rejection based on thresholding, enabling efficient decoding. Unlike discrete-variable QKD, which uses distinct photon states, CVQKD encodes information in continuous properties of light, such as amplitude and phase. The core focus is on reconciliation, a critical process for correcting errors introduced by noise and imperfections in the quantum channel. The research explores various error correction codes to establish a shared secret key, including Low-Density Parity-Check (LDPC) codes, Polar codes, Spinal codes, and rateless codes, each offering unique advantages in different scenarios. The study investigates methods to optimize performance, including increasing key rate, extending transmission distance, and reducing the Quantum Bit Error Rate (QBER). Key concepts explored include Gaussian modulation, trusted noise, de-randomization, pseudo-Random Graphs, and small-bias probability spaces. Real-time CVQKD with Efficient Error Correction Scientists have achieved a breakthrough in long-distance continuous-variable quantum key distribution (CVQKD) by developing a new error correction method that achieves a real-time key rate of at least 8% of the Devetak-Winter value, surpassing the performance of existing reconciliation schemes. This addresses a critical limitation in CVQKD, where signal degradation over long distances necessitates complex error correction that is often too slow for practical use.
The team’s approach utilizes random codebooks and a block rejection mechanism, enabling highly parallelizable decoding suitable for real-time systems. The research focused on improving error correction efficiency while maintaining security, a difficult balance in quantum communication. The method involves Alice sending blocks of coherent states, and Bob measuring the quadratures of these states, then concealing the measurements within a large table of random sequences. Alice then tests each entry in the table, using a similarity score to identify the correct one, accepting the block if a single score exceeds a predetermined threshold. Crucially, the accept/reject decisions are encrypted, preventing an eavesdropper from gaining information about the process and simplifying the security analysis. Experiments demonstrate the system’s capability at a distance of 300 kilometers, achieving a key rate of 8. 2% of the Devetak-Winter value, with a reconciliation efficiency of 0.059 at a loss of 60 decibels. This represents a significant advancement over previous systems, achieving real-time performance at a much greater distance.
The team’s approach allows for a key rate of 0.1 × 10^6 bits per second, and the method’s high level of parallelism makes it suitable for practical implementation in long-distance quantum communication networks.
Pseudorandom Codebooks Boost Long-Distance CVQKD This research presents a new method for error correction in long-distance continuous-variable quantum key distribution (CVQKD) systems.
The team developed a pseudorandom-codebook approach to reconcile information, addressing the challenge of low signal-to-noise ratios that typically hinder CVQKD over extended distances. This method is designed to be highly parallelizable, making real-time implementation more feasible, and predicts a key rate of at least 8% of a standard benchmark value, exceeding the performance of existing reconciliation schemes. The researchers demonstrated the practicality of this pseudorandom approach, even when applying conservative security assumptions related to key length. They achieved this by encrypting decisions made during error correction, avoiding the need to analyse complex, non-Gaussian states. While acknowledging that concealing the precise key length remains a challenge, they suggest combining QKD keys with post-quantum cryptography keys as a potential solution. The study also identifies areas for future investigation, including extending the method to discrete modulation, optimising quadrature discretization, performing a non-asymptotic analysis of the secret key rate, and accounting for excess noise in the communication channel. Furthermore, the team plans to explore optimized parallel implementations of the scheme to enhance its performance and efficiency. 👉 More information 🗞 Random coding for long-range continuous-variable QKD 🧠 ArXiv: https://arxiv.org/abs/2512.15990 Tags: