Real-time polarization control for satellite QKD with liquid-crystal beacon stabilization.

Area of Science:

• Quantum Information Science
• Optical Engineering
• Photonics

Background:

• Polarization instability poses a significant challenge for satellite quantum key distribution (QKD).
• Atmospheric effects and platform motion distort photon polarization, degrading entanglement fidelity.
• Accurate identification and compensation of polarization transformations are crucial before detection.

Purpose of the Study:

• To develop and evaluate a compact, fast polarization-compensation approach for satellite QKD.
• To utilize liquid-crystal (LC) variable retarders and a co-propagating reference signal for real-time polarization tracking.
• To assess the performance and impact of the LC-based system on QKD security.

Main Methods:

• Implementation of a liquid-crystal (LC) based polarimeter for real-time polarization tracking.
• Evaluation using direct and Fourier-based Stokes parameter reconstruction.
• Analysis of LC switching dynamics and polarimetric inaccuracies on QKD performance through simulations.

Main Results:

• Accurate polarization estimation achieved with a limited number of measurements, balancing speed and precision.
• Demonstrated compatibility with real-time applications by analyzing LC switching dynamics.
• Simulations show only a moderate increase in quantum bit error rate, maintaining secure key distribution.

Conclusions:

• Liquid-crystal (LC) based polarization control offers an efficient and practical solution for real-time compensation in satellite QKD.
• The developed system maintains entanglement fidelity and enables secure key distribution despite polarization distortions.
• This approach addresses a critical challenge in advancing satellite-based quantum communication technologies.