Northwestern University Sends Entangled Photons Through a Live Commercial Fiber Link
Researchers demonstrated quantum entanglement distribution over a 24.4-kilometer metropolitan fiber while it carried high-capacity internet traffic, achieving more than 94% fidelity.
Northwestern University scientists have taken quantum networks out of the lab, successfully sending quantum entanglement through a 24.4-kilometer fiber-optic cable connecting Evanston and downtown Chicago while the same cable simultaneously carried high-capacity commercial internet traffic, preserving entanglement with more than 94% fidelity.
The experiment, the first real-world distribution of quantum entanglement over a metropolitan fiber simultaneously carrying commercial internet traffic, addresses a fundamental obstacle: entangled photons are exquisitely sensitive, and the crosstalk from conventional data signals normally overwhelms the quantum correlations before they can be used.
Entanglement has until now been confined to carefully shielded setups, typically using dedicated dark fiber where nothing else is transmitted. The Northwestern team showed that the delicate quantum states can coexist with the high-bandwidth traffic of a working metropolitan network, a finding that could dramatically simplify the deployment of quantum communication infrastructure.
The 94% fidelity figure is well above the threshold required for practical applications such as quantum key distribution. That the link stretched 24.4 kilometers — enough to connect two major urban centers — suggests that existing fiber plants could underpin the first wave of metropolitan-scale quantum networks without the expense of laying new, dedicated cables.
What remains to be seen is how well this approach scales to longer distances and more complex topologies. But by proving that entanglement can travel on the same fibers that already carry the internet, the work removes one of the most persistent doubts about whether a quantum internet can be built on top of the one we already have.