Scientists have achieved an important milestone on the road to building a future quantum internet.
For the first time, researchers have successfully sent delicate quantum information through the same fiber-optic cable that was carrying large amounts of ordinary internet traffic, proving that both can operate together without interfering with each other.
The breakthrough was made by researchers at Northwestern University and published in the journal Optica Quantum.
The achievement could make it much easier and less expensive to build future quantum communication networks because it suggests they can use the fiber-optic cables that already exist instead of requiring entirely new infrastructure.
Quantum information is extremely fragile. Even tiny amounts of interference can destroy it, making it difficult to send over long distances.
Traditional internet traffic, on the other hand, is incredibly powerful and fills optical fibers with huge amounts of light signals carrying data.
The researchers compared the challenge to an ant trying to walk through a crowd of elephants. Despite this huge difference, they found a way for both types of signals to travel together safely.
In the experiment, the team generated pairs of entangled photons in their laboratory at Northwestern University’s Evanston campus.
Quantum entanglement is a unique property of quantum physics in which two particles remain linked even when they are separated by long distances. Changes to one particle are connected to the other, making entanglement a key building block for future quantum communication.
One photon from each entangled pair stayed in the laboratory, while its partner traveled through a 24.4-kilometer fiber-optic cable to downtown Chicago.
At the same time, the very same cable was carrying two high-speed internet data channels operating at 800 gigabits per second, along with additional traffic similar to what would be found on a busy commercial network.
Altogether, the fiber carried enough optical power to support about 36 terabits of data every second. According to the researchers, that is roughly equal to around 20 million YouTube videos being streamed at the same time through a single fiber.
Even under these demanding conditions, the quantum signals survived remarkably well. More than 94% of the quantum entanglement remained intact after the journey, showing that the fragile photons were still strongly connected despite sharing the cable with massive amounts of internet traffic.
The researchers achieved this by carefully separating the two types of signals. Modern internet communications usually operate in a part of the light spectrum known as the C-band. The team instead placed the quantum photons in a quieter region called the O-band, where they experienced much less interference. Special optical filters also helped reduce unwanted background noise.
Keeping the two ends of the network perfectly synchronized was another major challenge. Because the quantum signals traveled between two separate locations, the researchers needed timing accuracy measured in trillionths of a second. They accomplished this using an advanced optical timing system called White Rabbit, which allowed them to identify matching photon pairs with extraordinary precision.
The new experiment builds on earlier work by the same research group. In 2024, they demonstrated quantum teleportation over a 30-kilometer fiber cable inside a laboratory. While that showed the technology could work under controlled conditions, the latest study moves the research into a real telecommunications network carrying live, high-capacity traffic.
The researchers say this is an important step toward combining quantum technology with today’s communication systems. Rather than replacing existing internet infrastructure, future quantum networks may simply operate alongside conventional internet traffic using the same cables.
The team is now working toward an even bigger goal: demonstrating quantum teleportation between distant locations across a real metropolitan telecommunications network. While distributing entangled photons is the first step, actually transferring quantum information between remote sites is much more difficult.
Even so, this successful demonstration shows that the vision of a practical quantum internet is becoming increasingly realistic.
By proving that fragile quantum signals can safely share the same fiber as everyday internet traffic, the researchers have brought the next generation of secure, ultra-fast quantum communication one step closer to reality.
