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Twisted light has transmitted information across 143 kilometres of open space — almost 50 times further than the previous record. The breakthrough could revolutionise how we communicate with satellites.

Light is an electromagnetic wave that has crests and troughs. It also has a property called phase, which governs when the crests or troughs reach a particular point in space. Normally, all the waves that make up a beam of laser light have the same phase, so their crests or troughs are in sync.

Not so with twisted light: different parts of a twisted laser light beam have different phases, making the beam appear to move like a corkscrew. The amount of twists in the corkscrew can be used to encode information.

Crucially, there is no theoretical limit to how many twists you can encode in a single beam, and hence no limit to the amount of information you can store in it. This makes it ideal for communications, especially with satellites. But atmospheric turbulence can disrupt twisted light.

In 2014, at the University of Vienna in Austria and colleagues transmitted twisted light through the air over Vienna. They encoded enough information to send images of Mozart and Boltzmann.

Over the sea

But that was sent only 3 kilometres. The light would have to make it across tens if not hundreds of kilometres of free space without disruption if it were to be used for communications.

“We were interested in whether such beams can survive such long distances,” says Zeilinger’s colleague .

So the team went to the Canary Islands, where it transmitted a beam of twisted laser light 143 kilometres between islands: from the Roque de los Muchachos Observatory in La Palma to another observatory on Mount Teide in Tenerife. The researchers were also able to put the laser in a superposition of different twists at the same time, allowing it to encode more information.

They encoded the message “Hello World!” in the signal. It arrived with only one error — a “P” instead of a “!”.

The speed of encoding and decoding the message made this method slower than Morse code, and more like that of smoke signals. “We found this very amusing,” says Krenn.

But , who works on twisted light communications at the University of Southern California in Los Angeles, is impressed. “It really was a question. Could you go over long distances?” he says. “This is a wonderful demonstration to say, ‘Yes, you can’”.

The next step is to speed up the system using well-known techniques, such as adaptive optics, which can correct for atmospheric turbulence in real time. “It leads to a lot of excitement about where this is going,” says Willner.