A matter of consequence

14/08/1995
Down To Earth

A matter of consequence TILL recently, matter was for scientists a chimera that had 4 known faces -- solid, liquid, gas, and the lesser known plasma, a state of matter that materialises at extremely high temperatures. But 70 years ago, Einstein had posited a new state of matter existent at extremely low temperatures, very close to the theoretically unattainable absolute zero (-273.16 degree celsius). That elusive 5th state of matter has finally yielded to tenacious probing by scientists and researchers. The feat was achieved by a team of us scientists at the Joint Institute for Laboratory Astrophysics in Boulder, Colorado. The physicists cooled a cloud of rubidium metal atoms to within a whisker of absolute zero -- 300 times lower than has ever been achieved -- and then persuaded the whole group to behave as a single atom. Some scientists have described the finding as spectacular and breathtaking. "The term Holy Grail seems quite appropriate, given the singular importance of the discovery," wrote Oxford physicist Keith Burnett in the journal Science (July 14, 1995), which first reported the finding. Called the "Bose-Einstein condensate", the new matter is essentially a gas of atoms whose normal motion is virtually frozen by extreme cooling. In such a static condition, the wavelengths of the individual atoms grow to relatively enormous sizes, overlap each other and condense into a superjumbo atom. This oversized blob of matter represents a kind of bridge between the everyday world of normal objects and the ultra-small world of atoms and elementary particles. However, the blob still obeys the dictates of quantum mechanics -- which is, simply put, the science of the "behaviour" of subatomic particles. In the '30s, Albert Einstein picked up the work of the Indian physicist Satyendranath Bose and predicted the new state of matter. But achieving it then was impossible as atoms would have had to be cooled to about 180 billionths of a degree above absolute zero. This task created other difficulties. For instance, what vessel would you keep the new matter in at that temperature? What instrument would you use to see what you had achieved? Any material would transfer heat enough to destroy the evidence, and so would the light used to see it. Scientists at the University of Colorado held the rubidium atoms in a "bottle" of magnetic fields, and slowed them down with a technique called "laser cooling". They then devised a way to transfer the cooled atoms into a trap and bung them together into a lump. Fortunately, while the condensate was destroyed when a laser probe was flashed through it, it survived long enough to leave its image on the computer screen. Eric A Cornell, the leader of the Colorado team, described the Bose-Einstein condensate as a kind of matter analogous to a laser beam. In a beam of ordinary light produced by a flashlight, the wave-particles of energy known as photons behave chaotically in a variety of mismatched "quantum states". By contrast, the photons in a beam of laser light march in total synchrony with each other. Similarly, ordinary atoms in a cloud of gas exist in a chaotic state, but in the new matter they are coherently matched with each other. The scientists withheld the news of the discovery until the 3rd week of July to allow time for independent researchers to study and evaluate their results. At least 10 top scientific teams across the world were in the race for this Holy Grail of particle physics. But of what use will this new matter be? The Colorado team was a little cautious in suggesting an application for their discovery: "If you can get these things to move, then you could diffract them off electric or magnetic fields. By doing that, you could measure really fundamental constants, such as Planck's constant, and use them as probes for testing theories describing the bizarre nature of the subatomic world." Burnett, however, is more confident about the practical applications of the new matter. He says that the technology could lead to "extremely bright sources of atoms, an atomic laser that is bound to have many applications", possibly to construct ultra-small electronic circuits. Some scientists hope this phenomenon will make it easier to understand quantum mechanical phenomena such as superconductivity (the ability of some materials to conduct electrical current without any resistance) and superfluidity (the ability of certain fluids to flow through even the thinnest channels without resistance).

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