Spectral separation—quantum signals in the O-band while commercial traffic used the C-band—helped minimize interference and preserve entanglement.

The tested fiber carried two 800 Gbps data channels and demonstrated the capacity to transmit about 36 Tbps of classical data, illustrating coexistence of quantum and classical signals.

The experiment builds on a 2024 study that achieved quantum teleportation over a 30-kilometer laboratory fiber link and extends it into a real-world, noise-rich environment.

A real-world demonstration distributes quantum entanglement over 24.4 kilometers of installed fiber that also carries high-capacity classical telecommunications traffic, showing coexistence of quantum and classical signals in the same infrastructure.

Entanglement fidelity stayed above 94% even with full traffic and rose toward 99% when traffic was off, indicating the quantum link withstands realistic network noise; any imperfections were attributed to the photon source and equipment rather than the coexisting traffic.

After the 24.4-kilometer journey, entanglement fidelity remained above 94%, demonstrating that delicate quantum signals can survive in real telecommunications environments and stay entangled.

Key researchers include Prem Kumar as senior author and Gina Talcott as the study’s first author, with the work conducted at Northwestern University’s McCormick School of Engineering and Center for Photonic Communication and Computing.

The project is supported by the U.S. Department of Energy via Fermilab, underscoring ongoing efforts to integrate quantum technology with existing telecom infrastructure.

Precise, picosecond-level synchronization between Evanston and Chicago using the White Rabbit timing system enabled correct identification of entangled photon pairs in real time despite heavy traffic.

One photon of each entangled pair was sent from Evanston to downtown Chicago over the campus-to-city fiber link, with its partner remaining on campus, using two data channels at 800 gigabits per second to simulate heavy classical traffic.

Entangled photon pairs were generated on Northwestern University’s Evanston campus, with one photon traveling through Chicago’s fiber network to remain entangled at the destination.

To combat Raman noise from high classical traffic, the quantum signals traveled in the quieter O-band and were narrowly filtered to reject stray light, synchronized with a CERN-originating White Rabbit timing system to picosecond precision.