Number 233 (Story #1), July 14, 1995 by Phillip F. Schewe and Ben Stein BOSE-EINSTEIN CONDENSATION IN ATOMS has been achieved in a rubidium gas held in a tabletop atom trap. Eric Cornell of NIST (Boulder) and Carl Wieman of the University of Colorado and their colleagues begin by cooling a vapor to 10 micro-K using the pressure of opposing laser beams. With the lasers turned off, the atoms are further chilled by allowing the warmer atoms to evaporate away while the cooler atoms, confined by an innovative array of changing magnetic fields, sort themselves into a more compact bunch. At this point quantum mechanics comes into play in a dramatic way. Atoms are normally considered as particles but, according to quantum mechanics, they have wavelike properties too. Indeed, an atom has an equivalent wavelength, the deBroglie wavelength, which is inversely proportional to the atom's momentum. As atoms are cooled they slow down and their deBroglie wavelength gets larger. A prediction by Satyendra Bose and Albert Einstein made 70 years ago foresaw that at a low enough temperature the wavelength would exceed the inter-particle spacing and the atoms would begin to overlap. In terms of quantum mechanics the atoms would become indistinguishable and would, in effect, enter into a single quantum state. Over the years instances of a Bose-Einstein condensate (BEC) have been observed; superfluid helium-4 and superconductivity represent states of matter in which bosons (integral-spin particles) condensed into macroscopic quantum states. But the bosons in these systems interacted with each other and therefore, to better understand the BEC process, physicists have sought to effect a condensation in an ideal gas of noninteracting atoms. In recent years groups at MIT, Amsterdam, Stanford, and in Colorado have been racing to produce the requisite conditions of temperature and density. The NIST-Colorado physicists have now succeeded with a vapor of rubidium atoms dilute enough so that the atoms can be regarded as non-interacting. Their BEC state occurred at a temperature of 180 nK for periods as long as 15 seconds and consisted of a 20-micron glob of about 2000 atoms. Even in the process of ending the BEC state (by turning off the magnetic fields, which causes the atoms to disperse) the researchers could probe the condensate's properties. A laser snapshot of the just-released atoms allows one to determine the velocities of the particles just after the BEC condition has ended. The velocity distribution is highly peaked around zero velocity, as compared to a broad velocity distribution before the onset of BEC. This peaked velocity distribution is an important sign that BEC had been achieved. The temperature of the atoms just as they begin to disperse can also be estimated: the result, 20 nK, is essentially the lowest temperature for atoms ever recorded and arguably the coldest temperature in the universe. Regarding the unique nature of the BEC, Colorado physicist Michael Anderson says that "The condensate is to ordinary matter as laser light is to the light from a light bulb." That is, a sample of ordinary atoms (viewed as a quantum wave phenomenon) consists of a collection of unrelated waves, just as the light waves radiated by the randomly firing atoms in the filament of a light bulb are unrelated. In contrast, the atom waves in a BEC are related and therefore constitute a form of coherent matter, just as the light waves in a laser beam are part of a single coherent quantum state. A range of tests on the new bizarre state of matter is planned by the Colorado scientists, who expect the experiment to be repeated in other labs. Scientists at Rice University have apparently achieved BEC. (M.H. Anderson et al., Science, 14 July 1995. Journalists can obtain illustrations and lists of experts in this area by contacting AIP Public Information at physnews@aip.org.)