The Bose-Einstein Condensate

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The Bose-Einstein Condensate

#1  Postby RichardPrins » Mar 24, 2010 12:14 am

The Bose-Einstein Condensate
Eric A. Cornell and Carl E. Wieman wrote:
Three years ago in a Colorado laboratory, scientists realized a long-standing dream, bringing the quantum world closer to the one of everyday experience

Editor's Note: The main text of this article, originally published in the March 1998 issue of Scientific American, is being made available in light of the recent nomination of one of the authors, Carl Wieman, as associate director for science in the Office of Science and Technology Policy. Both authors won the Nobel Prize in Physics in 2001 for their discovery of the Bose-Einstein condensate. (Wolfgang Ketterle also shared the prize that year for his contributions.)

In June 1995 our research group at the Joint Institute for Laboratory Astrophysics (now called JILA) in Boulder, Colo., succeeded in creating a minuscule but marvelous droplet. By cooling 2,000 rubidium atoms to a temperature less than 100 billionths of a degree above absolute zero (100 billionths of a degree kelvin), we caused the atoms to lose for a full 10 seconds their individual identities and behave as though they were a single “superatom.” The atoms’ physical properties, such as their motions, became identical to one another. This Bose-Einstein condensate (BEC), the first observed in a gas, can be thought of as the matter counterpart of the laser—except that in the condensate it is atoms, rather than photons, that dance in perfect unison.

Our short-lived, gelid sample was the experimental realization of a theoretical construct that has intrigued scientists ever since it was predicted some 73 years ago by the work of physicists Albert Einstein and Satyendra Nath Bose. At ordinary temperatures, the atoms of a gas are scattered throughout the container holding them. Some have high energies (high speeds); others have low ones. Expanding on Bose’s work, Einstein showed that if a sample of atoms were cooled sufficiently, a large fraction of them would settle into the single lowest possible energy state in the container. In mathematical terms, their individual wave equations—which describe such physical characteristics of an atom as its position and velocity—would in effect merge, and each atom would become indistinguishable from any other.

ATOMIC TRAP cools by means of two different mechanisms. First, six laser beams (red) cool atoms, initially at room temperature, while corralling them toward the center of an evacuated glass box. Next, the laser beams are turned off, and the magnetic coils (copper) are energized. Current flowing through the coils generates a magnetic field that further confines most of the atoms while allowing the energetic ones to escape. Thus, the average energy of the remaining atoms decreases, making the sample colder and even more closely confined to the center of the trap. Ultimately, many of the atoms attain the lowest possible energy state allowed by quantum mechanics and become a single entity known as a Bose-Einstein condensate. MICHAEL GOODMAN

Progress in creating Bose-Einstein condensates has sparked great interest in the physics community and has even generated coverage in the mainstream press. At first, some of the attention derived from the drama inherent in the decades-long quest to prove Einstein’s theory. But most of the fascination now stems from the fact that the condensate offers a macroscopic window into the strange world of quantum mechanics, the theory of matter based on the observation that elementary particles, such as electrons, have wave properties. Quantum mechanics, which encompasses the famous Heisenberg uncertainty principle, uses these wavelike properties to describe the structure and interactions of matter. (...)
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