Light travels at a snail's pace

17 Jun 2002

A group of physicists has slowed down the velocity of light, by a factor of about 600 million, to below a slow walking speed.

Lene Hau, of the Rowland Institute for Science and Harvard University, told the recent meeting of American Association for the Advancement of Science that her group has made light travel at just 1 mile per hour (1.6 km/h) through a Bose-Einstein condensate.

A Bose-Einstein condensate is formed when a group of atoms is cooled to very close to absolute zero. At this temperature the velocity of the atoms is small and well defined. This means that their positions are uncertain and are spread out to overlap each other (because of Heisenberg's uncertainty principle). This medium has a very high refractive index.

Normally materials with high refractive indices absorb, rather than transmit, the light. The research group has avoided this by employing two laser beams that create an interference pattern and make the medium transparent at the frequency of the incoming light.

Last year the research group used a Bose-Einstein condensate to slow light to 38 miles per hour (60 km/h). The group aims to further reduce the speed of light to that of sound in the condensate (about 1 cm/s) and hopes that atoms can be induced to surf on the front of the light pulse.

Potential applications of such slow light include highly sensitive switches and low-power nonlinear optics for communications, signal processing, displays and night-vision devices.

SH