Oh, Vienna, plus image-carrying laser beam (Image: Mario Krenn)

MOZART and Schrödinger flew through the air over Vienna recently. Their digital images were encoded in twisted green light, marking an important step towards long-distance communication in free space.

Light offers the best way to communicate between Earth and orbiting satellites, but atmospheric turbulence can destroy the signal. Polarised light is resistant to the effects of turbulence, but polarised photons can carry only one bit of information apiece. So researchers have looked for other properties of light that could boost the bit rate.

One solution is twisted light, in which the wavefront of light spirals around a central axis as it travels. There is no limit to the number of twists for each photon, so they can theoretically store boundless amounts of information. Now, Mario Krenn, Anton Zeilinger and their colleagues at the University of Vienna in Austria have transmitted photons with four levels of twists, giving them the ability to transmit four bits of information.


Erwin Schrödinger, before and after his twisted flight (Image: Mario Krenn)

After digitising images of Mozart, Schrödinger and physicist Ludwig Boltzmann, the team encoded the data in twisted green laser light. Then they transmitted the beam from the top of a radar tower to a receiver 3 kilometres away – a record for twisted light transmission in the open air – where software read the patterns of light and decoded the images (arxiv.org/abs/1402.2602).

“It’s a huge technological achievement,” says Jonathan Leach, who studies twisted light at Heriot-Watt University in Edinburgh, UK. “It’s really amazing that they were able to transmit these quite faithful images across what’s quite a long free-space distance.”

It’s really amazing that they were able to send quite faithful images of Mozart and Schrödinger

The effective thickness of Earth’s atmosphere is only about 6 kilometres, so the demonstration is a big step on the way to using twisted light to communicate with satellites.

This article appeared in print under the headline “Twisted light transmits over record distance”