Bose - Einstein condensate

A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of weakly interacting bosons confined in an external potential and cooled to temperatures very near absolute zero (0 K or −273.16 °C). Under such conditions, a large fraction of the bosons occupy the lowest quantum state of the external potential, at which point quantum effects become apparent on a macroscopic scale.

This state of matter was first predicted by Satyendra Nath Bose and Albert Einstein in 1924–25. Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons). Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the Zeitschrift für Physik which published it. Einstein then extended Bose's ideas to material particles (or matter) in two other papers.

Seventy years later, the first gaseous condensate was produced by Eric Cornell and Carl Wieman in 1995 at the University of Colorado at Boulder NIST-JILA lab, using a gas of rubidium atoms cooled to 170 nanokelvin (nK) (1.7×10−7 K). For their achievements Cornell, Wieman, and Wolfgang Ketterle at MIT received the 2001 Nobel Prize in Physics. In November 2010 the first photon BEC was observed. (read more) (see more)

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You think that light is fast? Well, think again. Sometimes it is slower than a crawl. All schoolchildren know that light is the fastest thing there is. It zips along through empty space at 297,000 km per second (186,000 miles a second).

But now a Danish physicist and her team of collaborators have found a way to slow light down to less than 1.6 km per hour (one mile an hour) - slower than a slow walk.

The way Dr Hau and her team have slowed down light by a factor of 600 million or so is to use a group of atoms called a Bose-Einstein condensate (BEC). These atoms are cooled to a temperature of only a few billionths of a degree above absolute zero, the coldest possible temperature, at which all motion stops.

In a Bose-Einstein condensate, atoms are hardly moving at all. This means that according to the uncertainty principle that rules atoms, they are spread out and overlap. This results in a group identity for the collection of supercold atoms. And when light passes through such an environment, it will slow down.

By firing co-ordinated beams of laser light through the BEC, Hau and colleagues have slowed light down to a crawl. Inside the BEC, the so-called refractive index (which measures the slowing of light) becomes enormous: as high as 100 trillion times greater than that of glass. (news.bbc.co.uk)