Quantum internet signals travel over commercial fibre-optic using Internet Protocol on Verizon fibre

Researchers have demonstrated that quantum signals can be carried over standard, commercial fibre-optic links while still obeying the same Internet Protocol rules that route everyday online traffic.

This pushes the long-discussed idea of a quantum internet closer to reality by placing it on the very infrastructure that already delivers the modern web.

Where it happened

Working between two buildings in Philadelphia connected by roughly 1 kilometre (0.6 miles) of Verizon fibre, the researchers transmitted quantum states across ordinary telecoms cabling.

At the University of Pennsylvania School of Engineering and Applied Science (Penn Engineering), Liang Feng and colleagues showed that these quantum transmissions could be handled using familiar internet-style rules.

Feng’s Q-chip put a conventional, readable header in front of the quantum payload, enabling routers to make forwarding decisions without disturbing the delicate quantum state.

That approach addressed routing on an active fibre line, even though it did not eliminate the distance constraints that still prevent quantum networks from scaling broadly.

Quantum internet and routing

Quantum networking has typically relied on entanglement-a connection that links separated particles so that what happens to one influences the other.

By contrast, traditional routers repeatedly inspect data in transit, because reading a packet reveals where it needs to go next.

If a quantum state is measured directly, it cannot withstand that kind of handling: the measurement removes the very information the network must keep intact.

So, for a practical quantum network, the challenge is to determine routing information without ever reading the quantum portion itself.

How packets changed

Rather than treating quantum traffic as fundamentally incompatible with existing systems, the chip coupled the quantum transmission with a normal light signal that network equipment can safely read.

This leading header carried Internet Protocol-the addressing and routing framework behind everyday online communications-so established network management tools could still be used.

Because the readable header and the quantum payload were tightly synchronised on the chip, routing choices could be made in real time.

The significance is that quantum and classical traffic can share a common “language”, instead of requiring a separate network built from the ground up.

Reading around damage

In real-world conditions, fibre outside the laboratory warms and cools, vibrates, flexes, and bends-and those changes can knock quantum signals off their intended path.

Penn’s method monitored the classical header instead, since the same environmental disturbances shift both the classical and quantum signals in almost the same way.

“Because we can measure the classical signal without damaging the quantum one, we can infer what corrections need to be made to the quantum signal without ever measuring it, preserving the quantum state,” said Feng.

In effect, measurable noise became a useful reference, guiding corrections that would have destroyed the information if the quantum state had been inspected directly.

Numbers on fibre

Despite the noise on Verizon fibre, the connection maintained fidelity-a measure of how well the signal survives-at above 97%. In practice, that meant the quantum state typically arrived closely matching its form at the source.

Because the chip was made in silicon using established fabrication techniques, it also suggested a path towards manufacturing at meaningful scale.

That combination of strong performance and familiar materials made the work look more like a reusable platform than a one-off demonstration.

Importance of the quantum internet

According to applications described by the National Institute of Standards and Technology (NIST), quantum networks could enable more than security, including advanced sensors and networks of quantum computers.

Connected machines could share computational workloads across locations, and distributed sensors could compare the same event from multiple sites simultaneously.

These prospects help explain why engineers continue to pursue entanglement beyond carefully controlled environments and into public communications infrastructure.

Penn’s result did not deliver those applications yet, but it pointed to a practical route towards the sort of networks they would require.

Where distance wins

As the route length increases, the familiar problems return: quantum information still cannot be copied and boosted the way an ordinary optical signal can.

Conventional internet links deal with distance by using amplifiers, but amplification would disrupt the very quantum state being transmitted.

Instead, engineers need a quantum repeater-hardware designed to extend fragile quantum links-before trials can move from city-scale experiments to regional connections.

Until repeaters are mature, the most plausible near-term quantum networks will remain local, dense, and carefully engineered.

Not just keys

Earlier fibre-based work had already demonstrated the delivery of specialised quantum keys over long distances, so Penn’s team was not starting from scratch.

However, those systems primarily targeted secure codes, rather than connecting remote quantum processors through shared entanglement.

Penn’s packet-based design mattered because it focused on networking quantum states themselves, not simply safeguarding a classical message.

That difference separates secure communication alone from the more demanding goal of building a true quantum network.

Scaling networks for quantum internet

Up to now, the demonstration connected a single server to a single node across two buildings, rather than covering an entire city.

“We’ve taken a key step toward larger-scale experiments and a practical quantum internet,” said Feng.

By deploying additional chips on existing urban fibre, the concept could grow without waiting for a completely new cable build.

That framing makes the work feel less like a distant forecast and more like a field test for how early quantum infrastructure could be rolled out.

The experiment suggests the next challenge is no longer basic compatibility with fibre, but the practical task of expanding beyond a single link.

If quantum repeaters, control software, and more chips follow, quantum networking could begin travelling through the same streets as the internet people already use.