Digital Signal Processing from Classical Systems Advances Continuous-Variable QKD Performance, Reviewing 220 Publications

Digital signal processing techniques, originally developed for conventional communication systems, now play a crucial role in advancing the field of continuous-variable quantum key distribution (CV-QKD). Davi Juvêncio Gomes de Sousa, Caroline da Silva Morais Alves, Valéria Loureiro da Silva, and Nelson Alves Ferreira Neto, from QuIIN and SENAI CIMATEC, present a comprehensive review exploring how these established methods are being adapted and refined for quantum communication. Their work demonstrates that algorithms such as Kalman filtering and adaptive equalization, traditionally used in classical systems, prove effective in addressing key challenges within CV-QKD, including phase synchronization and noise mitigation. This systematic analysis not only maps the current landscape of cross-domain techniques, but also identifies promising innovations and persistent technical barriers, ultimately supporting the development of more secure and scalable quantum communication networks.

Local Oscillators and Fiber Distance Limits

Research into continuous-variable quantum key distribution (CV-QKD) consistently focuses on building practical systems and overcoming real-world limitations. Extending the range of CV-QKD over fiber optic cables is a key area of investigation, with researchers tackling signal loss and dispersion. Improvements to hardware components, such as homodyne/heterodyne detectors and polarization control systems, also receive considerable attention. Researchers are actively developing techniques to increase key rates, including multiplexing strategies like polarization, frequency, and time-division multiplexing.

Maintaining system accuracy and stability over time requires advanced calibration and stabilization methods. Security analysis and protocol development remain crucial, with researchers providing rigorous security proofs and developing countermeasures against potential attacks. Improving the efficiency and security of error correction codes, such as polar codes and direct reconciliation, is essential for extracting secure keys. The choice of modulation and encoding schemes significantly impacts CV-QKD performance, with polar modulation being a common approach. Understanding the communication channel and the noise that affects quantum signals is paramount.

Researchers are modeling and analyzing terahertz channels, indoor environments, and the effects of atmospheric turbulence. Advanced techniques and emerging concepts are pushing the boundaries of CV-QKD, with machine learning and neural networks being used to predict key rates and optimize system parameters. Efficient error correction and the stability of local oscillators are consistently identified as critical areas for improvement.

CV-QKD Analysis Using DSP Techniques

Recent research systematically investigates the application of digital signal processing (DSP) techniques, originally developed for coherent optical communication, to continuous-variable quantum key distribution (CV-QKD). Researchers employed a rigorous methodology, adapted from the PRISMA protocol, to ensure a comprehensive and reproducible synthesis of this emerging field. This approach provides a focused evaluation of how DSP techniques are being applied to CV-QKD. The research team meticulously extracted data from selected publications, identifying commonly adopted DSP strategies and the performance metrics used to evaluate their effectiveness.

This involved examining how classical DSP algorithms, such as Kalman filtering, carrier recovery, and adaptive equalization, were adapted for use in the quantum regime. Researchers documented the modifications required to account for the unique security and noise constraints inherent in CV-QKD systems. The study also identified recent DSP innovations in coherent optical communication, assessing their potential for future integration into CV-QKD systems.

DSP Enhances Continuous-Variable Quantum Key Distribution

A systematic review demonstrates how digital signal processing (DSP) techniques, originally developed for coherent communication systems, are being successfully adapted for continuous-variable quantum key distribution (CV-QKD). Researchers employed a rigorous methodology, adapted from the PRISMA protocol, to ensure a reproducible and systematic analysis of the field. The analysis reveals that classical DSP algorithms, including Kalman filtering, carrier recovery, and adaptive equalization, have been successfully adapted for use in CV-QKD systems, often requiring modifications to account for security and noise constraints. The study highlights the successful integration of machine-learning-assisted signal estimation techniques, demonstrating their potential to improve system performance. Researchers identified recent DSP innovations in coherent communication, such as neural equalization, probabilistic shaping, and joint retiming-equalization filters, as promising candidates for future integration into CV-QKD systems. Researchers identified that challenges remain in achieving robust phase tracking under ultra-low Signal-to-Noise Ratio (SNR) conditions, a critical factor for long-distance quantum communication.

Signal Processing Boosts Quantum Key Distribution

A systematic review demonstrates how digital signal processing (DSP) techniques, originally developed for coherent communication systems, are being successfully adapted for continuous-variable quantum key distribution. Researchers systematically analyzed recent work, identifying numerous instances where established algorithms, such as Kalman filtering and adaptive equalization, have been modified and implemented within quantum key distribution systems. The findings reveal that these adaptations significantly improve performance in critical areas including phase synchronization, polarization tracking, and the mitigation of excess noise, all of which are essential for reliable quantum communication. The study highlights a convergence between classical signal processing and quantum technologies, paving the way for more robust and scalable continuous-variable quantum key distribution systems. While substantial progress has been made, challenges remain in achieving reliable phase tracking under extremely low signal-to-noise ratios and in real-time polarization compensation.