Scientists have taken a step towards the quantum Internet – for the first time, quantum and ordinary photons were transmitted over one optical fiber

The capabilities of quantum computers will increase when they begin to be connected in networks. And it will be great if these networks are built on existing fiber-optic channels. This will be cheaper, and in addition it will increase the security of ordinary information transmission channels. Another thing is that “quantum” photons and ordinary ones do not combine well in one channel, because quantum states are sensitive to interference and are easily destroyed, but in Germany they have learned to cope with this.

Image source: Leibniz University Hannover

The experiment was carried out by scientists from the University of Hannover. Leibniz (Leibniz University Hannover). It was supposed to show that quantum information and classical digital information can be transmitted over the same optical fiber. Potentially, this will mean an absolutely hack-proof regular Internet, as well as the combination in the future of several quantum computers into clusters to solve problems unimaginable in complexity today.

«To make the quantum internet a reality, we need to transmit entangled photons over fiber optic networks, explains physicist Michael Kues from the University of Hannover. Leibniz. “We also want to continue to use optical fibers for general data transmission. Our research is an important step towards combining the conventional Internet with the quantum Internet.”

Image source: Science Advances 2024

To combine a quantum and conventional optical signal in one channel, the scientists used a homemade modulator with a linear change in phase or delay (the so-called serrodyne). Serrodine phase shifts the optical signal in the optical fiber (in one frequency channel) to accommodate both quantum and classical data. Experience has shown that this does not destroy the entanglement of photons. At the output, in the same way, the streams are divided into quantum and conventional for processing each at its own receiver.

Let us emphasize that everything happens in one frequency channel, and not just in a fiber, where there can be dozens or even hundreds of frequency channels. This will reduce conventional bandwidth slightly, paving the way for the faster emergence of the quantum internet.