Distance no worries for spooky particles
Scientists have used quantum physics to zap an encrypted message more than 140 kilometres between two Spanish islands.
Professor Anton Zeilinger from the University of Vienna and an international team of scientists used 'spooky' pulses of light to send the message.
They say this is an important step towards making international communications more secure.
Zeilinger described the study this week at the Australian Institute of Physics meeting in Brisbane.
The photons they sent were linked together through a process known as quantum entanglement.
This means that their properties remained tightly entwined or entangled, even when separated by large distances, a property Einstein called spooky.
The group's achievement is important for the emerging field of quantum cryptography, which aims to use properties such as entanglement to send encrypted messages.
Research groups around the world are working in this field. But until now they have only been able to send messages relatively short distances, limiting their usefulness.
Zeilinger's team wants to be able to beam the messages to satellites in space, so they could theoretically be relayed anywhere on the planet.
To test their system, the team went to Tenerife in the Canary Islands, where the European Space Agency operates a telescope specifically designed to communicate with satellites.
Instead of pointing the telescope at the stars, Zeilinger says, the scientists turned it to the horizontal and aimed it towards a photon sending station 144 kilometres away on the neighbouring island of La Palma.
"Very broadly speaking, we were able to establish a quantum communication connection," he says.
"We worried a lot about whether atmospheric turbulence would destroy the quantum states. But it turned out to work much better than we feared."
The results suggest it should be possible to send encrypted photons to a satellite orbiting 300 or 400 kilometres above the Earth, he says.
"This is our hope. We believe that such a system is feasible."
The next step is to try the system out with an actual satellite, a project which is likely to involve the European Space Agency and others.
"This is about developing quantum communications on a grand scale,"
His team expects to publish its results soon.