Northwestern team distributes quantum entanglement over 24 km of busy Chicago fiber

Researchers at Northwestern University report the first demonstration of quantum entanglement distribution between distant nodes over installed telecommunications fiber that was simultaneously carrying high-capacity commercial traffic, according to SciTechDaily coverage of a study in Optica Quantum. A photon carrying quantum information traveled more than 24 kilometers, including a 24.4-kilometer fiber path, from Northwestern's Evanston campus toward downtown Chicago while sharing the cable with ordinary internet signals. The quantum connection retained more than 94% fidelity, the report said. Senior author Prem Kumar, a Northwestern electrical and computer engineering professor and director of the Center for Photonic Communication and Computing, said quantum signals are tiny compared with classical signals and compared the journey to an ant among elephants. Graduate student Gina Talcott is the study's first author. The work is framed as a step toward quantum networks that reuse existing fiber rather than requiring separate systems. Kumar said the team showed entanglement distribution and that transferring information in a full teleportation sequence remains a further, harder step. The research was supported by the U.S. Department of Energy via Fermilab. Laboratories seeking metro-scale quantum links gain evidence that entanglement can coexist with live classical traffic on shared plant, reducing the case for dedicated dark fiber for early network tests.