Twisted beams of light sent across Vienna

The city of Vienna has been the site of an outdoor experiment, in which twisted beams of light were transmitted over a large distance for the first time.

If a light beam of a certain colour or wavelength is twisted into a corkscrew shape, the amount of data it can transmit can increase dramatically, depending on the number of turns in the corkscrew.

The twisting characteristic is known as orbital angular momentum (OAM). Researchers have shown in the past that it can be used to transmit 2.5 terabits of data per second - more than 66 DVDs – through an optical fibre.

But in some forms of communication, such as Earth to space satellites, optical fibres cannot be used. Researchers have been attempting to send twisted light over free space, while avoiding air turbulence.

In the experiment, researchers from the University of Vienna and Institute for Quantum Optics and Quantum Information, sent twisted light from a green laser beam through a lens on top of a radar tower at the meteorology institute to the University of Vienna, a distance of three kilometres.

The researchers encoded the light with images of Wolfgang-Amadeus-Mozart, Ludwig Boltzmann and Erwin Schrodinger.

"The OAM of light is theoretically unbounded, meaning that one has, in theory, an unlimited amount of different distinguishable states in which light can be encoded," said co-author of the study Mario Krenn.

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