Credit: Shutterstock
Scientists have sent quantum photons through a live section of the internet network and watched them arrive intact on the other end.
Researchers at Northwestern University sent pairs of entangled photons through a 24.4-kilometer fiber-optic cable connecting their Evanston campus to downtown Chicago. At the same time, that same cable was carrying internet traffic. Despite the noise, the quantum signal held together. More than 94% of the entanglement survived the trip. Later, the team published this success in the journal Optica Quantum.
This is the first time researchers used a fiber network that was, at that same moment, carrying live commercial internet traffic. Earlier experiments of this kind were done inside a lab or on a dedicated fiber cable network.
What the Researchers Did?
Quantum entanglement links two particles so closely that measuring one instantly tells you something about the other, no matter how far apart they are. It is one of the basic building blocks scientists need to create quantum networks, which could eventually support highly secure communication and computing systems that work across multiple locations.
For this experiment, the team generated pairs of entangled photons in a lab on Northwestern’s Evanston campus. One photon from each pair stayed in the lab. Its partner traveled 24.4 kilometers through an already-installed fiber line to the StarLight International/National Communications Exchange Facility in downtown Chicago.
A few numbers stand out from the experiment:
- The cable carried two active 800 Gigabits per second internet data channels.
- The fiber supported a simulated total data capacity of up to 36 Terabits per second.
- The experiment maintained more than 94% entanglement fidelity.
- The photons were synchronized with timing precision within trillionths of a second.
Keeping the Quantum Signal From Getting Lost
Quantum signals depend on single photons. Ordinary internet traffic uses light made of millions of photons at once. Putting both on the same cable risks burying the fragile quantum signal under the much stronger classical traffic.
To prevent that, the researchers moved their quantum photons into the O-band, a quieter section of the light spectrum. Regular commercial traffic stayed in the C-band, the range most telecom systems already use. Keeping the two types of signals in separate bands reduced interference between them.
The team also had to solve a timing problem. Because the entangled photons were split between two sites 24.4 kilometers apart, researchers needed a reliable way to confirm which arriving photon belonged to which original pair. They used an optical timing system called White Rabbit to synchronize both locations to within trillionths of a second. That level of precision let them match photon pairs correctly even with heavy traffic running through the same fiber.
Prem Kumar, the study’s senior author and a professor of electrical and computer engineering at Northwestern, described the size difference between the two types of signals in simple terms. In his words, “It’s like an ant traveling through a path filled with elephants.”
Why This Result Matters
Building a large-scale quantum network from scratch would be costly. It would likely require laying new, dedicated fiber lines separate from the cables already carrying the world’s internet traffic.
This experiment points to a cheaper path forward. It shows that quantum signals can share existing commercial fiber with regular internet traffic, as long as the two are separated by wavelength and synchronized with enough precision. That means future quantum networks could potentially be built using existing infrastructure, instead of requiring an entirely new physical network.
The work builds on an earlier study by the same research group in 2024, which achieved similar results inside a lab using a 30-kilometer cable. This new experiment moved that method out of the lab and into a live, two-site network under real-world conditions.
What to Expect Next
Distributing entanglement is only the first step toward a working quantum network. The next goal is Quantum Teleportation, a process that transfers quantum information between two distant points without physically moving the particles carrying it.
Teleportation happens in two stages. First, entanglement has to be distributed between the two locations, which is what this experiment demonstrated. Second, the actual information has to be transferred using that entanglement, a more difficult step the team has only performed in the lab so far.
The researchers say their next goal is to perform full Quantum Teleportation between Evanston and Chicago over a live commercial network, building directly on what this study proved is possible.
