Cold changed our lives in last century. Without cold, we would not have supermarkets, or the Space Shuttle. In the Antarctic, the coldest temperature on Earth, -80 ° C, is found at the south pole. The attempt to reach absolute zero in the latter part of the 19th century involved liquefying gases. James Dewar designed the Dewar flask (thermos) to conduct his experiments. Faraday had liquefied nitrogen but could not create liquid oxygen, hydrogen or other gases. Dewar admired Faraday, and continued his liquefying experiments using pressurized gases. He had no success, and finally the Dutch scientist van der Waals explained why — pressure was not enough. The atoms needed other types of cooling. Several gases were liquefied, but liquid H2 was elusive.
Heike Kamerlingh Onnes, Dewar’s rival, built an industrial size lab. Both researchers used a cascade of gases that liquefied at lower and lower temperatures. At the final stage, hydrogen was pressurized to 180 atmospheres and cooled to -252° . This process was risky because glass could explode with low temps & high pressures. In fact, explosions occurred repeatedly. Dutch officials ordered Onnes’ lab in Leiden closed. In 1898, Dewar had been working for 20 yrs. and finally produced 20 cm3 H2. Liquid oxygen froze in the liquid H2. But helium had been discovered on Earth, and it still need to be liquefied. It was predicted to liquefy at 5° above absolute zero.
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In 1908, Onnes was finally ready to liquefy helium. The temperature stuck below the liquefaction of H2. Onnes realized that they had done it, and he won the Nobel price. Disappointed, Dewar stopped his low-temperature research and moved to another field. The Leiden lab investigated electric conduction at very low temperatures. At 4 ° above absolute 0, mercury conducted electricity with no resistance. Onnes termed this property superconductivity. In the 1930s, 2° above absolute zero was reached and helium evaporation stopped. The helium became a superfluid that could leak through materials, e.g. glass, that normally would hold it. It had zero viscosity and could climb the vessel’s walls. It could also produce a frictionless fountain that never stopped flowing.
Meanwhile, in the 1920s, quantum theory had begun to emerge. In 1925, a new state of matter was predicted — the Bose-Einstein condensate, which occurred just above absolute 0. The condensate followed quantum theory’s wavelike properties. Huge waves were formed, overlapping, and the material was both at rest and present everywhere at once. Several research groups attempted to make B-E condensate.. Kleppner at MIT tried to use magnetism with H2 atoms. At the University of Colorado, Weiman & Cornell used a laser to cool larger atoms such as rubidium and cesium by tuning the laser to the correct speed and trapping the particles in a magnetic field. In this way they were able to reach a few millionths of degree above absolute 0. Ketterle, also at MIT, used higher densities, pushing towards a condensate using sodium atoms. However, they needed one more cooling technique — evaporative cooling. In 1995 the Boulder, Colorado thought they had made the condensate, but they wanted to check it out. At 170 billionth of a degree above absolute zero, they made a very small amount of B-E condensate. Soon afterwards Ketterle’s lab produced larger amount. Cornell, Ketterle & Weiman shared Nobel prize in 2001 for physics. In 1998, Kleppner had also succeeded.
The new challenge was to determine what to use the condensate for. Lene Hau at Harvard used the Bose-Einstein condensate to slow down light from its normal speed to the speed of bicycle. The light was compressed, but the information in it was still present and could be retrieved. Currently, researchers are making prototype quantum computers. For example, Lloyd at MIT has made atoms into computers which do not work on the 0 and 1 principle of bits. Instead, they use qbits, which can be both a zero and a 1 working in parallel. This type of device has been used to map the magnetic activity of brain.
