Bose-Einstein condensate

A Bose-Einstein condensate is a gaseous superfluid phase formed by atoms cooled to temperatures very near to absolute zero. The first such condensate was produced by Eric Cornell and Carl Wieman in 1995 at the University of Colorado at Boulder, using a gas of rubidium atoms cooled to 170 nanokelvins (nK). Under such conditions, a large fraction of the atoms collapse into the lowest quantum state, producing a superfluid.

Slowing light

Despite our inability to fully understand these new states of matter, several interesting properties have already been observed in experiments. Bose-Einstein condensates can be made to have an extremely high gradient in optical density. Normally, condensates do not have a particularly special refractive index, due to having an atomic density far less than normal solid materials. However, additional pump lasers can be used at frequencies designed to alter the state of atoms in the Bose-Einstein condensate, increasing drastically the index for a beam of a precise target frequency recorded at a probe point. This results in an extremely low measured speed of light within the condensate; some have slowed beams of light down to mere meters per second, speeds which can be exceeded by a human on a bicycle. This apparent speed of light is slower than c, since although it travels at the speed of light between the atoms, it is absorbed by the atoms for a long time before being re-emitted, so giving at outward appearance of travelling slowly.

Related Topics:
Optical density - Lasers - Bicycle - Speed of light

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A rotating Bose-Einstein condensate could be used as a model black hole, allowing light to enter but not to escape. Condensates could also be used to "freeze" pulses of light, to be released again when the condensate breaks down. This is done by shutting off the pumping lasers with pulses still in transit and allowing the photons to be absorbed. Reapplying the pump lasers can then release the pulses of light, and due to the coherence of the Bose-Einstein condensate, there may be very little degradation. Research in this field is still young and ongoing.

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