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Q: Fachverband Quantenoptik und Photonik

Q 81: Quantum Communication, Networks, Repeaters, & QKD III

Q 81.1: Vortrag

Freitag, 6. März 2026, 14:30–14:45, P 10

Device-independent quantum key distribution in an event-ready atom-photon architecture over 25 km fiber using double frequency conversion — •Jonas Meiers, Christian Haen, Max Bergerhoff, Tobias Bauer, Christoph Becher, and Jürgen Eschner — Universität des Saarlandes, Experimentalphysik, 66123 Saarbrücken, Germany

Quantum cryptographic protocols offer physical security through no-cloning or entanglement. Following the device-independent quantum key distribution protocol of [1], we present our event-ready implementation based on entanglement between a single atom and its emitted photons. The protocol requires four atomic bases and two photonic bases and allows us to create a quantum key with security verification via the Bell parameter. We employ polarization entanglement between a single trapped ⁴⁰Ca⁺ ion and an emitted photon at 854 nm, generated on the P_3/2 → D_5/2 transition via Raman scattering [2]. The photon is frequency-converted to the telecom band, enabling its transmission over a 25-km-long, polarization-stabilized fiber spool, and afterwards reconverted to 854 nm before state projection. The projected qubits enable key generation after classical post-processing, including error correction and privacy amplification. Future applications include our 15-km-long urban fiber as quantum link, that has already been characterized and demonstrated [3].
[1] R. Schwonnek et al., Nat. Commun. 12, 2880 (2021)
[2] M. Bock et al., Nat. Commun. 9, 1998 (2018)
[3] S. Kucera et al., npj Quantum Inf. 10, 88 (2024)

Keywords: Quantum communication; Trapped ion; Atom-photon entanglemet; Quantum key distribution