spaceSpace and Physics

Quantum Communication Has Been Achieved Underwater For The First Time


Robin Andrews

Science & Policy Writer

This is what quantum entanglement looks like. (Not really.) sakkmesterke/Shutterstock

China is really investing heavily in quantum shenanigans. They’ve recently launched the world’s first quantum satellite, and now they’ve dived underwater to test out a submarine version too.

Essentially, both experiments have been testing a phenomenon known as quantum entanglement. It’s far more complicated than we’re letting on, but essentially, two particles can sometimes act as a pair when they are separated by huge distances. Their behaviors mirror each other, and together, they act as a single particle.


When you measure one of these particles in any way, you will only see the characteristics of the whole system. Despite not being able to “transmit” information between each other in any way, the particles appear to “know” what the other is doing at any point in time.

This decidedly spooky behavior has many applications, but one such use is in communications. Instead of sending information directly over long distances, say from Earth to space, or from one segment of the seafloor to another, you just have two entangled particle systems that “know” the state of each other.

As entangled systems can only be viewed as a collective whole, rather than their individual parts, any information contained within them is theoretically impossible to ascertain without being on either end of the “line” of communication. That’s why cybersecurity experts are so keen to get a quantum communications system up and running.

It’s already officially been achieved via satellite by Chinese researchers, and now it seems that they’ve also managed it underwater too. Writing in the journal Optics Express, a team from Shanghai Jiao Tong University in China explain how they achieved it.


“Underwater communication is vital for undersea exploitation and modern communication,” the authors note in their study, before noting that “conventional ways which employ acoustical technique for underwater communication have their drawbacks,” including, of course, their increasing lack of security. This new experiment set out to fix this.

In the future, submarines could secretly talk to each other via quantum entanglement. u3d/Shutterstock

It began with shooting a beam of light into a specially designed crystal. The crystal splices the light into pairs of photons that are entangled. This is essentially what was achieved during the related satellite experiment, but it's a lot easier to maintain an entangled system in air and the vacuum of space.

Water, which is far denser than air, is trickier to maintain quantum systems in. The researchers decided to give it a go by setting up a small tank of seawater in their laboratory, and ultimately, they succeeded, making their work a world first.

The tank was only as wide as a couple of standard desks put together though, and as you’re probably aware, the sea is far more voluminous and sizable than that. At this point then, it’s hard to tell how important this study actually is – and, as ever, more work is needed to clarify the results.


[H/T: New Scientist]


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