These atoms are cooled to a temperature of only a few billionths of a degree above absolute zero, the coldest possible temperature, at which all motion stops.

BBC: A Bose-Einstein condensate: It slows down light

Since what matters is not just the absolute temperature level but the rate of change as well, it makes sense to try to slow down the increase.

ECONOMIST: Blowing hot and cold

Their tool, the Bose-Einstein condensate, is a superchilled soup of matter that can be created only when the temperature is near absolute zero.

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This slows down the movement, and hence the temperature, of its atoms to a fraction of a degree above absolute zero.

ECONOMIST: An old thought experiment may soon be realised