Quantum state of light teleported 30 kilometres through fibre optic cable amid internet traffic

In 2024, researchers in the US managed to teleport a quantum state of light through more than 30 kilometres of fibre optic cable while the same link carried a heavy stream of live internet traffic - a technical milestone that had previously been viewed as out of reach.

It is not the sort of breakthrough that will let you “beam” to work to dodge the morning rush, or make your favourite cat videos download any quicker.

Even so, teleporting quantum states across today’s real-world communications infrastructure is a major step towards a quantum-connected computing network, stronger encryption, and new approaches to sensing.

"This is incredibly exciting because nobody thought it was possible," says Prem Kumar, a Northwestern University computing engineer who led the study.

Watch the clip below for a summary of their research:

"Our work shows a path towards next-generation quantum and classical networks sharing a unified fiber optic infrastructure. Basically, it opens the door to pushing quantum communications to the next level."

Quantum teleportation through fibre optic cable amid internet traffic

Quantum teleportation can sound a little like a Star Trek transport system, where people appear to vanish and reappear elsewhere in an instant. In practice, the process takes the quantum “menu” of possibilities for an object in one place and - by deliberately destroying that original state - imposes the same balance of possibilities on a comparable object located somewhere else.

Although measuring the two objects locks in their outcomes at the same moment, establishing the entangled relationship between them still depends on sending a single wave of information from one point in space to another.

Why a single photon is so hard to protect

A quantum state is fragile: more like fairy floss caught in a spring shower than something solid and stable. Soon after it is created, it is at risk of collapsing into an ordinary, definite reality. Radiation in the form of electromagnetic waves, along with the constant thermal jostling of moving particles, rapidly strips away quantum behaviour through decoherence unless the state is protected.

Keeping quantum states sheltered inside a computer is difficult enough. Trying to send a single photon down optical fibres already buzzing with bank transactions, cat videos, and text messages - while still preserving that photon’s quantum state - is substantially more intimidating. It is akin to tossing that delicate quantum fairy floss into the Mississippi and hoping it still tastes the same at the far end.

How the team reduced interference on a 400 gigabit-per-second link

To help their solitary photon hold on to its state in the face of a 400 gigabit-per-second flood of internet data, the researchers used multiple methods to constrain the photon’s channel and lower the likelihood that it would scatter and mingle with other waves.

"We carefully studied how light is scattered and placed our photons at a judicial point where that scattering mechanism is minimized," says Kumar.

"We found we could perform quantum communication without interference from the classical channels that are simultaneously present."

Other teams had previously shown - in internet-style simulations - that quantum information could be sent alongside classical data streams. Kumar’s group, however, was the first to demonstrate quantum-state teleportation alongside a genuine, live internet stream.

Each successful test adds weight to the idea that a quantum internet is unavoidable, giving computing engineers a new set of tools to measure, monitor, encrypt, and calculate in ways we have not previously been able to - and crucially, without having to rebuild the internet from scratch.

"Quantum teleportation has the ability to provide quantum connectivity securely between geographically distant nodes," says Kumar.

"But many people have long assumed that nobody would build specialized infrastructure to send particles of light. If we choose the wavelengths properly, we won't have to build new infrastructure. Classical communications and quantum communications can coexist."

This research was published in Optica.

An earlier version of this article was published in December 2024.