Ultra-secure quantum data sent over existing internet cables

Another step towards a quantum internet has been completed, and it doesn’t require any special communications equipment. Two data centres in Germany have exchanged quantum secure information using already existing telecommunication fibres at room temperature. This is in contrast to most quantum communications, which often require cooling to extremely low temperatures to protect quantum particles from disturbances in their environment.

The quantum internet, where information can be exchanged extremely securely thanks to being encoded into quantum particles of light called photons, is quickly making forays into the world outside the lab. In March, a microsatellite enabled a quantum link between ground stations in China and South Africa. A few weeks earlier, the first operating system for quantum communication networks was unveiled.

Now, Mirko Pittaluga at Toshiba Europe Limited and his colleagues have sent quantum information through optical fibre between two facilities around 250 kilometres apart in Kehl and Frankfurt, Germany. The information also passed through a third station between them, a little over 150 kilometres from Frankfurt.

Photons can get lost or corrupted as they traverse long distances through fibre optic cables, so large iterations of the quantum internet will require “quantum repeaters”, which will mitigate those losses. In this set-up, the midway station played a similar role, allowing the network to outperform previously tested and simpler connections between the two endpoints.

In a notable improvement on previous quantum networks, the team used existing fibre, as well as devices that can be easily slotted into racks that already house traditional telecommunications equipment. This strengthens the case for the quantum internet eventually becoming a plug-and-play operation.

The researchers also used photon detectors that are much less costly than those used in past experiments. Though some of those previous experiments spanned hundreds of kilometres more, the use of these detectors brings down both the cost and energy requirements of the new network, says Raja Yehia at the Institute of Photonic Sciences in Spain.

Prem Kumar at Northwestern University in Illinois says that using the type of quantum communication protocol they have here on commercially available equipment underscores how quantum networks are approaching practicality. “A systems engineer could look at this and see that it works,” says Kumar. However, to be fully practical, the network would have to exchange information faster, he says.

Mehdi Namazi at the quantum communication start-up Qunnect in New York says this approach could be beneficial for future networks of quantum computers or quantum sensors, but it is still not as efficient as if it included a true quantum repeater.