Curator's Take
This article demonstrates that entanglement between a single atom and a near‑visible photon can be distributed across a metropolitan‑scale fiber link by converting the photon to the telecom S‑band and back with only a sub‑percent loss in fidelity. By achieving a 1.7 % overall photon transfer efficiency over 24 km of deployed fiber, it directly tackles the longstanding wavelength mismatch between atomic quantum nodes and existing communication infrastructure. The work builds on recent low‑noise quantum‑frequency converters and brings hybrid atom‑photon networks one step closer to practical quantum repeaters and city‑wide quantum internet applications. While the link efficiency still needs improvement for large‑scale deployment, the proof‑of‑concept shows that integrating atomic memories with commercial fiber is now experimentally viable.
— Mark Eatherly
Summary
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 14km line-of-sight via 24km of a deployed commercial fiber. The photon at wavelength 780nm 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.