A team of European researchers have proposed a series of experiments that, if successful, could turn the International Space Station into a key relay for a quantum communications network.
The key basis of physics underlying quantum communications is entanglement. Entangled particles are connected in a way that pretty much defies common sense. If you change the spin of one of the particles, the spin of its entangled counterpart will change - even if they're miles apart. And that change happens nearly instantaneously - at least four orders of magnitude faster than the speed of light, according to a recent experiment.
Quantum networks, though, are often fragile - and as a result, quantum communications networks have so far been maxed out at about 90 miles distance. That's because the weather can interfere with the entangled states of the photon. As a consequence, researchers have begun looking into the possibility of space-based quantum communication, so that there's less chance of atmospheric interference.
But why bother with these networks at all if they're so fragile? The answer is pretty simple - because they're almost perfectly secure. Here's how it works. Let's say that I want to send a message to New York City. My message is going to travel through normal channels, but it will be encrypted with a key. That key is transmitted via the entangled photons - so the changes I make to entangled particles on my end almost instantly show up in the particles in New York. We then compare the measurements of what I changed in my photons to those states in New York City.
Those measurements then comprise an encryption key for our communications. So even if our communications are bugged, nobody can read them without knowing that encryption key. And here's the important thing: if somebody were to try to eavesdrop on the quantum entanglement, they would alter the spin of the photons. So the measurements I make and the measurements made in New York would be out of sync - thus letting us know that we have an eavesdropper. It also prevents us from creating an encryption key, so we don't send any communications. Theoretically, a quantum encrypted network is almost perfectly secure. (That said, they're not perfect, and there are some exploits.)
In a paper published in this week's New Journal of Physics, the scientists from the Institute of Physics outlined their plans for a series of experiments involving the International Space Station as a quantum communications relay. The experimental setup is actually pretty simple - it would involve adding a photon detector to the camera that already exists on the bottom of the station. (One of the cameras that takes those gorgeous photos of Earth.) A series of entangled photons would then be sent at regular intervals to the station.
"According to quantum physics, entanglement is independent of distance. Our proposed Bell-type experiment will show that particles are entangled, over large distances -- around 500 km -- for the very first time in an experiment," said co-researcher Professor Ursin in a statement. "Our experiments will also enable us to test potential effects gravity may have on quantum entanglement."
If it works, that means that a quantum communications network could be built using the International Space Station as a relay to send quantum encryption keys over long distances. And the cost would only be a slight modification to the cameras already there, rather than building out an entire satellite network.
Right now, this is just a proposal - there are no plans for an experiment yet. But if they get the go ahead and resources to perform their experiment, it wouldn't take long for it to happen.
"We envision setting up the experiment for a whole week and therefore having more than enough links to the ISS available," said Ursin.
