Physics
How shining light on an atom makes it colder
Aim laser light against an atom's motion and each packet of light it absorbs acts as a tiny brake, so the atom slows and its temperature falls. Steven Chu's team used this to slow atoms to about 10 centimetres a second, work that shared the 1997 Nobel Prize in Physics.
Sources & further reading
The Royal Swedish Academy of Sciences / NobelPrize.orgThe Nobel Prize in Physics 1997: Press releaseThe Nobel committee's announcement of the prize for cooling and trapping atoms using laser light.Stanford University (Stanford Report)Steven Chu wins Nobel Prize for research on the interplay of light and atomsStanford's account of how Steven Chu's team slowed atoms to a crawl with crossed laser beams, called optical molasses.Plus Magazine, University of CambridgeAtomic clocks and laser coolingA Cambridge explainer on how cooling atoms with lasers makes the ultra-accurate clocks behind GPS.National Coordination Office for Space-Based PNT (GPS.gov), U.S. governmentGPS and Telling TimeThe U.S. government explainer on how GPS carries atomic-clock time and why power grids, phone networks, and markets depend on it.National Institute of Standards and Technology (U.S. Department of Commerce)NIST Launches a New U.S. Time Standard: NIST-F2 Atomic ClockNIST's announcement of the NIST-F2 fountain clock, accurate to about one second in 300 million years.American Physical Society (APS News)June 5, 1995: First Bose-Einstein CondensateThe physics-history record of the first Bose-Einstein condensate, made by cooling rubidium atoms with lasers and then evaporation.
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