Scientists have achieved quantum teleportation over a busy Internet cable for the first time

Scientists from Northwestern University, USA, are the first in the world, they claim, to carry out quantum teleportation over an Internet cable loaded with extraneous traffic. They managed to transmit the entangled states of two photons over a distance of 30.2 km over the same optical fiber through which ordinary data was exchanged, and then recorded the fact of the collapse of the wave function and the instantaneous teleportation of a quantum state.

Image source: AI generation Kandinsky 3.1/3DNews

There are still serious doubts about whether it is possible to use ordinary communications to transfer quantum states – in other words, to create a global quantum Internet without deploying a new separate infrastructure. The work of US researchers, published today in the journal Optica, suggests that quantum data could be transmitted over existing optical communication lines.

The experiment was carried out in the laboratory on a reel of optical cable 30.2 km long. Looking ahead, we note that at the next stage, scientists will try to teleport quantum states through a real Internet network. In laboratory conditions, the researchers, as far as possible, reproduced the operation of the Internet under normal conditions. The cable carried Internet traffic with a bandwidth of 400 Gbit/s in the C-band. The main task was to select such a frequency range for two entangled photons that their states would not be destroyed before measurement (before completion of transmission to the other end of the line). Scientists have also developed a filter system to minimize interference from normal traffic.

«This is incredibly exciting because no one thought it was possible,” said Northwestern’s Prem Kumar, who led the study. “Our work shows the way to next-generation quantum and classical networks sharing a single fiber-optic infrastructure. Essentially, this opens the door to taking quantum communications to the next level.”

It should be clarified that quantum teleportation does not transfer information in the traditional sense. The quantum state of the photon is unknown in advance. An attempt to determine it before transmission, for example to measure the direction of the spin, will lead to the collapse of the wave function, and then there will simply be nothing to send. And since we don’t know what we are transmitting, there is no point in teleported information. However, it is possible to teleport quantum states, which is the basis of quantum cryptography. If such a message is intercepted, it will be known instantly, regardless of the distance between the entangled photons.

Experimental design. Image source: Optica 2024

Scientists from Northwestern University have demonstrated that entangled photons can be transmitted simultaneously with regular data using a traffic-loaded conventional fiber optic line as an example. The quantum state is retained until the end of the transmission and is teleported when measured. This opens up the possibility for the coexistence of quantum cryptography and traditional Internet traffic. But researchers intend to go further. They are interested in transferring entangled states to other pairs of photons so that they can participate in distributed quantum computing. This is the only way to superimpose the quantum internet onto the existing internet infrastructure.