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arXiv · 2501.08891

Time-bin encoding quantum key distribution in free-space horizontal links during nighttime and daytime

Sebastiano Cocchi·Domenico Ribezzo·Giulia Guarda·Pietro Centorrino·Tommaso Occhipinti·Alessandro Zavatta·Davide Bacco
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Abstract

Free-space quantum key distribution (QKD) represents a groundbreaking advancement in secure communication, enabling secure key exchange over vast distances and offering robust encryption for the future quantum internet. However, the compatibility between fiber and free-space infrastructures continues to pose challenges for QKD protocols. Indeed, free-space and fiber-based networks commonly use different wavelengths and qubits encoding schemes. On the one hand, free-space QKD typically exploits visible light for its beneficial beam divergence compared to longer wavelengths, and polarization encoding for its robustness against turbulence. On the other hand, fiber-based QKD employs infrared light, particularly the C-band, because it shows the minimum losses with silica fibers, and time-bin encoding, due to polarization instability in optical fibers. In our study, we demonstrate the viability of a time-bin encoded QKD protocol operating in the C-band through horizontal turbulent free-space channels. We test the setup into a 50 m and a 500 m long links, achieving an average secure key rate of, respectively, 793 kbps and 40 kbps over several hours of measurements. The results encourage further exploration of the interoperability between free-space and fiber-based infrastructures, opening new possibilities for connecting terminal users with satellites in hybrid infrastructures.

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Sebastiano Cocchi, Domenico Ribezzo, Giulia Guarda, Pietro Centorrino, Tommaso Occhipinti, Alessandro Zavatta, Davide Bacco. 2025-01-15. Time-bin encoding quantum key distribution in free-space horizontal links during nighttime and daytime. https://arxiv.org/abs/2501.08891

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