Scientists see the light then make it disappear
Email Print Normal font Large font Deborah Smith
February 8, 2007

IT'S THE ultimate trick with light. Scientists have succeeded for the first time in extinguishing light in one spot and then making it reappear somewhere else.

This unprecedented control over light could pave the way for superfast computers and totally secure communication systems.

University of Sydney physicist Stephen Bartlett said the research by an American team was an important step towards the development of light-based technologies.

Nothing travels faster than light, which travels from the sun to Earth in only eight minutes, but scientists want to slow it down so they can better manipulate it.

Researchers led by Lene Hau at Harvard University had their first success in 1999, when they reduced the speed of light by 20 million fold, to 60kmh by passing it through a cloud of very cold gas (just above minus 273C).

In 2001 her team brought light to a dead stop in a similar cloud, known as a Bose-Einstein condensate.

For the new study, published overnight in the journal Nature, Professor Hau created two condensates a tiny distance apart. When a laser light pulse was beamed into one it slowed to a halt, as expected. But the light was then completely converted to matter, which travelled over to the second condensate at a leisurely pace of 200 metres an hour.

The original light pulse was reincarnated in that condensate, and went on its way. Professor Hau said the fact that the light was momentarily present as matter in the tiny gap between the condensates was very important, because matter was easy to manipulate, unlike light.

Michael Fleischhauer, of the Technical University of Kaiserslautern in Germany said: "It looks rather like black magic, but it is just quantum mechanics."

Dr Bartlett said the light could be extinguished in one condensate and revived in the other because, at the quantum level, atoms of the same kind are indistinguishable, no matter how far apart they are. "You have to think of the two condensates as one condensate in two different places."

Superfast quantum computers based on light would be able to handle huge amounts of information, for example to better model climate change.

Deborah Smith

http://www.smh.com.au/news/world/scientists-see-the-light-then-make-it-disappear/2007/02/07/1170524163468.html