Quantum internet promises ultra-secure, next-generation communications, but is it actually feasible on a global scale?
Absolutely, according to a new experiment carried out between satellites in orbit and a station on the ground.
The team of scientists was able to exchange several carefully managed photons in pulses of infrared light, carried between Russian GLONASS satellites and the Space Geodesy Centre on the ground run by the Italian Space Agency.
Getting these signals to pass through some 20,000 kilometres (12,427 miles) of air and space without any interference or data loss is no easy task – but the signs are promising that such a global network could indeed be functional.
"Space quantum communications (QC) represent a promising way to guarantee unconditional security for satellite-to-ground and inter-satellite optical links, by using quantum information protocols as quantum key distribution (QKD)," says one of the researchers, Giuseppe Vallone from the University of Padova in Italy.
The quantum key distribution or QKD method Vallone mentions refers to data encrypted using the power of quantum mechanics: thanks to the delicate nature of the technology, any interference is quickly detected, making QKD communications impossible to intercept.
In fact, hacking into a quantum mechanics message would cause it to self-destruct.
So far so good in theory, but keeping these secure channels open across long distances has proved tricky.
The key to the successful data exchange here was the use of passive retro-reflectors mounted on the satellites to keep the long-distance light signals intact, breaking the previous record distance for this type of quantum communication by an extra 15,000 kilometres (9,321 miles).
While satellites placed higher in orbit, like the GLONASS ones, are more difficult to communicate reliably with, they pass within sight of ground stations more regularly, potentially enabling an unhackable quantum network that can span the globe.
We're only just getting started with this type of technology – not least because scientists are still trying to figure out if it can actually work – and for the moment it's not clear exactly what a quantum internet would be used for or how it might be operated.
One idea is that it might become a specialised, very secure extension to the normal internet, used by a small selection of apps and devices.
What we do now know is that quantum communications are possible between the ground and high orbit satellites, extending the potential reach of the new technology.
That's important as the satellite networks we rely on continue to get developed and upgraded.
"Satellite-based technologies enable a wide range of civil, scientific and military applications like communications, navigation and timing, remote sensing, meteorology, reconnaissance, search and rescue, space exploration and astronomy," says Vallone.
"The core of these systems is to safely transmit information and data from orbiting satellites to ground stations on Earth. Protection of these channels from a malicious adversary is therefore crucial for both military and civilian operations."
The research has been published in Quantum Science and Technology.