Time-bin encoding quantum key distribution in free-space horizontal links during nighttime and daytime
Year: 2025
Authors: Cocchi S., Ribezzo D., Guarda G., Centorrino P., Occhipinti T., Zavatta A., Bacco D.
Autors Affiliation: Univ Firenze, Dipartimento Fis, Via Giovanni Sansone 1, Sesto Fiorentino, Italy; CNR INO, Largo Enrico Fermi 6, Florence, Italy; Univ Aquila, Dept Phys & Chem Sci, Laquila, Italy; European Lab NonLinear Spect LENS, Sesto Fiorentino, Italy; Galileo Galilei Inst Theoret Phys GGI, Largo Enrico Fermi 2, Florence, Italy; QTI Srl, Largo Enrico Fermi 6, Florence, Italy.
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 with 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 link, respectively achieving an average secure key rate of 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. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Journal/Review: OPTICA QUANTUM
Volume: 3 (4) Pages from: 346 to: 350
More Information: European Research Council (101077917); European Commission (PE00000014, 101091561, 101091408); Consiglio Nazionale delle Ricerche (501100004462).KeyWords: Long; Daylight; SecurityDOI: 10.1364/OPTICAQ.553977
