Self-stabilized high-dimensional quantum key distribution on a metropolitan free-space link

• URL: http://arxiv.org/abs/2602.22102v1
• Date: Wed, 25 Feb 2026 16:51:05 GMT
• Title: Self-stabilized high-dimensional quantum key distribution on a metropolitan free-space link
• Authors: Karolina Dziwulska, Christopher Spiess, Sarika Mishra, Markus Leipe, Yugant Hadiyal, Fabian Steinlechner,
• Abstract summary: We demonstrate high-dimensional time-bin-encoded quantum key distribution over a hybrid metropolitan link.<n>We implement both 2- and 4-dimensional protocols, and obtain estimated secure finite-key rates of (95 +- 28) kbit/s for 4D at (25.0 +- 2.0) dB loss.<n>Our results thus establish a practical and versatile platform for hybrid free-space-to-fiber quantum communication.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-sa/4.0/
• Abstract: Quantum communication technologies capable of operating reliably across heterogeneous optical channels are essential for scalable metropolitan quantum networks. Here we demonstrate high-dimensional time-bin-encoded quantum key distribution over a hybrid metropolitan link comprising 1.7 km free-space transmission and 685 m of optical fiber. Operating at a clock rate of 500 MHz in the C-band, we implement both 2- and 4-dimensional protocols, and obtain estimated secure finite-key rates of (95 +- 28) kbit/s for 4D at (25.0 +- 2.0) dB loss and (59 +- 27) kbit/s for 2D at (23.5 +- 2.3) dB loss. Crucially, we achieve continuous operation over 48 h in a fully self-referenced architecture: initial synchronization, interferometric phase stabilization, and long-term drift compensation are performed exclusively using the detected quantum signals, without auxiliary optical reference channels. Our results thus establish a practical and versatile platform for hybrid free-space-to-fiber quantum communication and show that the encoding dimensionality can be adapted to the optimal operating regime of realistic metropolitan channels, providing a pathway toward efficient, autonomous and deployable quantum network nodes.

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