Quantum information is notoriously fragile. Internet traffic is anything but. Yet Northwestern University scientists have demonstrated they can peacefully coexist inside the same fiber-optic cable.

In a new study, researchers successfully sent entangled photons through a 24.4-kilometer (15.2-mile) fiber-optic cable connecting Evanston and downtown Chicago while the same cable simultaneously carried high-capacity internet traffic. Even amid the torrent of conventional data, the quantum signals remained remarkably intact—preserving entanglement with more than 94% fidelity.

By allowing fragile quantum signals and powerful classical data streams to share the same optical fiber, the work demonstrates a practical path toward building future quantum networks without requiring entirely new communications infrastructure.