Savitzky-Golay Filter-Based Phase Recovery for CV-QKD
March 2024 – Elisabeth Llanos presented Luxquanta’s research paper “Savitzky-Golay Filter-Based Phase Recovery for CV-QKD” at the OFC Conference as the first author. The study was conducted under the supervision of Luxquanta’s lead Optical Design engineer, Dr. Samael Sarmiento, with the collaboration of Pol Adillon, PhD Student.
Quantum Key Distribution
Quantum Key Distribution (QKD) is a complex, multi-layered technology that harnesses the fundamentals of quantum mechanics to generate and distribute symmetric cryptographic keys between two parties without using mathematical algorithms. The keys generated are future-safe and resistant to all types of computational attacks, even those of future Quantum Computers.
Unlike DV-QKD, Continuous Variable QKD (CV-QKD) encodes the information in the X- and P-quadratures of the electromagnetic field of light, removing the need for single-photon detectors, which need to be operated at very demanding temperature conditions. Instead, CV-QKD employs coherent detectors that can be implemented with off-the-shelf telecom components.
Among the different parameters to work on, Phase Noise is one of the critical parameters to optimize. Its reduction is not just a technical challenge, but by reducing the amount of Phase Noise, we can enable the technology to cover greater distances, ultimately increasing the amount of real-use cases where CV-QKD technology could be deployed.
The main objective of the present paper, led by Dr Sarmiento as lead researcher and mainly carried out by Luxquanta’s PhD students Elisabeth Llanos and Pol Adillon as first authors, is to enhance the correction of phase noise by using a filtering technique not used before in CV-QKD scenario.
When comparing the excess noise and the SKR obtained when using SG or UKF filter, preliminary results show that SG outperforms the state-of-the-art UKF filter in CV-QKD scenarios.
The results show that positive SKR values could be obtained up to 48 km and 41 km for the SGF and UKF, respectively. When no phase estimation filters are used, the distance limit is 36 km.
In addition to the above results and the overall better performance of SG filters, the authors also argue that, based on the study results, a more profound system optimisation would allow the link to reach even longer fibre distances of up to 100km or more.