Researchers Entangles 780nm Photons with Atoms Across 24km Fiber

Researchers led by Maya Büki and 11 other authors have successfully distributed quantum entanglement between an atom and a photon using 24 kilometers of existing commercial fiber, a distance comparable to a metropolitan area. The team reports demonstrating this link with a 780nm photon, a near-visible wavelength that bypasses the typical telecom wavelengths required for long-distance transmission, bridging a critical gap between atomic quantum nodes and established networks. This achievement involved converting the photon’s wavelength twice, first to create entanglement with the atom and again for efficient fiber transmission, resulting in a 1.7% photon transfer efficiency with less than 1% affecting the atom-photon entanglement fidelity. The researchers write that entanglement distribution is the overarching purpose of quantum networks, suggesting this method brings practical, integrated quantum technologies closer to reality.

Successfully distributing quantum entanglement over metropolitan distances has moved closer with a demonstration of entanglement distribution via 24 kilometers of fiber between an atom and a photon at 780nm, a wavelength challenging for long-distance transmission. Researchers overcame this hurdle by employing two custom-built, low-noise quantum-frequency converters, enabling communication via 24 kilometers of existing commercial fiber optic cabling. This approach bypasses the need for entirely new infrastructure, a significant step toward practical quantum networks, and allows for the integration of atomic quantum nodes with long-distance fiber networks, opening possibilities for new applications in quantum information processing.

Despite the two conversion stages and substantial fiber length, the experiment yielded a 1.7% photon transfer efficiency 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.