https://doi.org/10.1140/epjqt/s40507-025-00306-9
Brief Report
Intermodal quantum key distribution field trial with active switching between fiber and free-space channels
1
Dipartimento di Ingegneria dell’Informazione, Università degli Studi di Padova, via Gradenigo 6B, IT-35131, Padova, Italy
2
ThinkQuantum s.r.l., via della Tecnica 85, IT-36030, Sarcedo, Italy
3
Padua Quantum Technologies Research Center, Università degli Studi di Padova, via Gradenigo 6A, IT-35131, Padova, Italy
Received:
8
February
2024
Accepted:
2
January
2025
Published online:
16
January
2025
Background: Intermodal quantum key distribution enables the full interoperability of fiber networks and free-space channels, which are both necessary elements for the development of a global quantum network. We present a field trial of an intermodal quantum key distribution system in a simple 3-node heterogeneous quantum network — comprised of two polarization-based transmitters and a single receiver — in which the active channel is alternately switched between a free-space link of 620 m and a 17 km-long deployed fiber in the metropolitan area of Padova.
Findings: The performance of the free-space channel is evaluated against the atmospheric turbulence strength of the link. The field trial lasted for several hours in daylight conditions, attesting the interoperability between fiber and free-space channels, with a secret key rate of the order of kbps for both the channels.
Conclusions: The quantum key distribution hardware and software require no different strategies to work over the two channels, even if the intrinsic characteristics of the links are clearly different.
Key words: QKD / Quantum network / Free-space optical communication
© The Author(s) 2025
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