Entangled Photons Survived a Fiber Stuffed With Internet Traffic
Picture a single ant trying to walk a road as a herd of elephants stampedes down it. Those are the odds facing a quantum signal inside a fiber-optic cable that’s also carrying regular internet traffic. The ant is one photon. The elephants are the millions of photons hauling your video calls and downloads. Prem Kumar at Northwestern used exactly that image to describe what his team just pulled off, and the surprising part is that the ant made it.
In a study published in Optica Quantum, Kumar’s group, with graduate student Gina Talcott as first author, sent entangled photons down a 24.4-kilometer fiber running from Evanston to downtown Chicago. Same cable, same moment, two 800-gigabit data channels blasting through it, plus enough extra power to stand in for a fully loaded commercial link. Kumar put the load at 36 terabits per second, or “roughly 20 million YouTube videos streaming simultaneously through a single fiber.”
The entanglement came out the far end above 94% fidelity. They say it’s the first time anyone has distributed entanglement between two remote nodes on a fiber carrying real commercial traffic.
How entangled photons survived commercial internet traffic
A quantum signal is a single photon. A classical signal is a flood of them. Drop one delicate photon into that flood and the noise should swallow it instantly.
So how do you protect the ant? According to the Northwestern report on July 22, you have to make two moves. First, the team parked the quantum photons in a quiet stretch of the spectrum called the O-band, and kept the internet traffic penned in the C-band where commercial gear already lives. Different neighborhoods on the same street. Second, they synchronized both ends of the link to within trillionths of a second, using a timing system named White Rabbit, so they could pick out matching entangled pairs in real time against all that background racket.
Why this isn’t a quantum internet yet
Here’s the part to keep straight, because it’s easy to oversell. What they did is entanglement distribution. That’s the first of two steps in quantum teleportation, and it’s the easier one. Kumar is blunt about it. You distribute entanglement, then you transfer the information, and the second step is harder than the first. Nobody teleported anything across Chicago here.
What makes it a genuine step forward is the realism. Their 2024 result worked in the lab, and this one ran on installed city fiber doing its actual job, which is a far less forgiving place to be a lone photon. The next goal is full teleportation over a metro network that’s still carrying commercial traffic.
So no quantum internet yet. Just proof that a quantum internet, if it arrives, might not need its own separate cables. The ant can share the road. (The Department of Energy, through Fermilab, paid for most of the trip.)