Improving Free-Space Continuous Variable Quantum Key Distribution with Adaptive Optics
Mikhael T. Sayat, Marcus Birch, Michael Copeland, Elisa Jager, Oliver Thearle, Francis Bennet, Ping Koy Lam, Nicholas J. Rattenbury, John E. Cater
Published: 2025/9/15
Abstract
A significant performance inhibitor of free-space continuous variable quantum key distribution (CVQKD) is turbulence, which gives rise to wavefront phase and amplitude aberrations. We demonstrate that in a turbulent channel, during coherent state transmissions from a continuous-wave laser, that the interferometric visibility between the local oscillator (LO) and quantum signal decreases. A solution to this is incorporating adaptive optics at the receiver to correct phase and amplitude aberrations in the wavefronts of the received quantum signal. We demonstrate the increased interferometric visibility and decrease in its fluctuations in a 60 cm and 30 m turbulent channel when using adaptive optics through channel characterisation. In an ideal CVQKD system, we show that this leads to more precise and larger positive secret key rates, improving the performance of free-space CVQKD in turbulent channels.