Curator's Take
AI Commentary
This article marks the first time entanglement swapping has been achieved across a five‑node relay while sharing the same C‑band fibers with live 10‑Gbps classical traffic, demonstrating that quantum repeaters can coexist with today’s telecom infrastructure. By quantifying the fidelity‑Raman‑noise trade‑off and showing successful swapping over four × 10 km spans, the work provides a concrete roadmap for integrating quantum links into existing backbone networks rather than requiring dedicated dark fibers. The result brings practical, large‑scale quantum networking—and its promised secure communication and distributed sensing capabilities—closer to real‑world deployment.
— Mark Eatherly
Summary
Quantum networks are resources for scaling quantum computers and distributed sensing technologies while offering post-quantum security benefits. Teleporting non-classical resources like entanglement, via so called entanglement swapping, is essential for networks in particular overcoming rate-loss limits via quantum repeaters. Deploying these systems on real infrastructure will likely require multiplexing photonic qubits into fibers carrying 'classical' light encoding standard Internet communications and control plane signals for multi-node quantum protocols. Here, we report the first demonstration of entanglement swapping and conventional communications operating over the same fibers. Entanglement is swapped across a five-node quantum relay topology connected by four long-distance fibers, each populated with classical data signals. Time-bin entangled photons in the C-band are multiplexed alongside C-band classical signals using dense-wavelength division multiplexing, introducing noise photons generated by high-power classical light. We experimentally and theoretically characterize the trade-off between quantum fidelity and Raman noise photons. Entanglement swapping is demonstrated over a maximum fiber length of 40 km (four 10-km fibers) while simultaneously transmitting 10-Gbps classical data through all fibers. These results represent a significant advancement in the demonstrated complexity of coexisting quantum and classical networks and provide a roadmap for achieving the widespread deployment of advanced quantum technologies.