Lasers Cool Atoms Toward Absolute-Zero

Although lasers often heat materials during processes such as cutting, carefully tuned laser light can also cool atoms, molecules, and small mechanical systems toward absolute zero. In Doppler cooling, opposing beams make moving atoms absorb more photons traveling against their motion, gradually reducing their momentum, speed, and kinetic energy. In 1978, teams at the National Institute of Standards and Technology and the University of Washington first demonstrated laser cooling on magnesium and barium ions. The technique now supports precise atomic clocks, spectroscopy, and atom-based quantum computing.

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