Intermodal quantum key distribution over an 18 km free-space channel with adaptive optics and room-temperature detectors

• URL: http://arxiv.org/abs/2602.16680v1
• Date: Wed, 18 Feb 2026 18:21:12 GMT
• Title: Intermodal quantum key distribution over an 18 km free-space channel with adaptive optics and room-temperature detectors
• Authors: Edoardo Rossi, Ilektra Karakosta-Amarantidou, Matteo Padovan, Marco Nardi, Marco Avesani, Francesco Bruno Leonardo Santagiustina, Marco Taffarello, Antonio Vanzo, Stefano Bonora, Giuseppe Vallone, Paolo Villoresi, Francesco Vedovato,
• Abstract summary: Intermodal quantum key distribution at telecom wavelengths provides a hybrid interface between fiber connections and free-space links.<n>We demonstrate a real-time intermodal quantum key distribution field trial over an 18 km free-space link.<n>An adaptive optics system, implementing direct wavefront sensing and high-order aberration correction, enables efficient single-mode fiber coupling.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Intermodal quantum key distribution at telecom wavelengths provides a hybrid interface between fiber connections and free-space links, both essential for the realization of scalable and interoperable quantum networks. Although demonstrated over short-range free-space links, long-distance implementations of intermodal quantum key distribution remain challenging, due to turbulence-induced wavefront aberrations which limit efficient single-mode fiber coupling at the optical receiver. Here, we demonstrate a real-time intermodal quantum key distribution field trial over an 18 km free-space link, connecting a remote terminal to an urban optical ground station equipped with a 40 cm-class telescope. An adaptive optics system, implementing direct wavefront sensing and high-order aberration correction, enables efficient single-mode fiber coupling and allows secure key generation of 200 bit/s using a compact state analyzer equipped with room-temperature detectors. We further validate through experimental data a turbulence-based model for predicting fiber coupling efficiency, providing practical design guidelines for future intermodal quantum networks.

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