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Metropolitan Entanglement Distribution between an Atom and a Near-Visible Photon

Maya Büki1,3,*, Pooja Malik2,3,*, Florian Fertig2,3, Tobias Frank1,3, Marvin Scholz1,3, Tommy Block2,3, Gianvito Chiarella1,3, Yiru Zhou2,3, Emanuele Distante1,3,† et al.

Pau Farrera1,3,‡, Gerhard Rempe1,3, and Harald Weinfurter1,2,3,§

  • *These authors contributed equally to this work.
  • †Present address: LENS—European Laboratory for Non-linear Spectroscopy and Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via Sansone 1, 50019 Sesto Fiorentino (Firenze), Italy.
  • ‡Contact author: pau.farrera@mpq.mpg.de
  • §Contact author: h.w@lmu.de
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Phys. Rev. Lett. 137, 090803 – Published 26 August, 2026

DOI: https://doi.org/10.1103/94hz-xtht

Abstract

Entanglement distribution is the overarching purpose of quantum networks. While communication over long distances can use deployed fiber infrastructure, it requires photons in the telecom band. However, advanced quantum network nodes do not operate at such wavelengths. Here we overcome this limitation with two tailor-made low-noise quantum-frequency converters to distribute entanglement between a single atom and a resonant photon over 14 km line of sight via 24 km of a deployed commercial fiber. The photon at wavelength 780 nm is first entangled with the atom, then converted to the telecom S-band, and finally back-converted after propagation through the fiber. This link enables a photon transfer efficiency of 1.7% while affecting the atom-photon entanglement fidelity by less than 1%. This brings integration of atomic quantum nodes with existing long-distance fiber networks into reach, enabling novel applications in quantum information processing.

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Outline

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Phys. Rev. Lett. 137, 090803– Published 26 August, 2026
  • Received 12 February 2026
  • Revised 8 May 2026
  • Accepted 24 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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