Quantum entanglement survived inside a fiber carrying ordinary internet traffic

Northwestern researchers say they sent entangled photons through 24.4 km of installed fiber between Evanston and downtown Chicago while the same fiber carried ordinary high-capacity data traffic, preserving more than 94% fidelity. The point is a real-world coexistence demonstration, not the launch of a consumer quantum internet service.

What Was Demonstrated

The team sent entangled photons through 24.4 km of installed fiber between Northwestern’s Evanston campus and the StarLight facility in downtown Chicago. The same fiber carried two 800-gigabit-per-second data channels plus optical power representative of a fully loaded commercial link. Northwestern says entanglement fidelity stayed above 94% under those conditions.

What The Paper Shows

The Optica Quantum paper describes O-band polarization-encoded entanglement distribution coexisting with C-band classical communications and a picosecond-level L-band synchronization signal. The researchers kept ordinary communications in the C-band, moved the quantum photons into a quieter O-band region, and used narrow filtering plus a White Rabbit timing system. The paper reports preserved entanglement under C-band conditions suitable for 36 Tbps transmission.

Why It Matters

A major practical barrier for quantum networks is the cost and complexity of deploying separate dark fiber. This result shows a path for quantum signals and existing telecom infrastructure to share the same fiber. Over time, that could matter for secure communication, distributed quantum computing, and quantum sensing that need to connect beyond isolated laboratories.

What It Is Not

This is an entanglement distribution demonstration. It is not completed quantum teleportation across a city network, and it is not a consumer quantum internet service. Northwestern says the next step is to perform quantum teleportation between remote nodes across a real-world telecommunications network. Distance, multiple nodes, operational reliability, and standards remain open problems.

What To Check Next

Use the Northwestern release to verify the 24.4-km route, above-94% fidelity, and ordinary data-traffic conditions. Use the Optica Quantum paper and author manuscript to check the O-band/C-band separation, two 800-Gbps channels, 36-Tbps operating context, and synchronization method. The headline should stay with entanglement distribution, not imply commercial deployment.

Official sources

Northwestern release: 24.4-km route, above-94% fidelity, and next step

Optica Quantum paper: journal record, DOI, and experimental conditions

arXiv manuscript: O-band/C-band coexistence, 36-Tbps context, and methods