Rubidium atoms used to record coldest temperature — ever

A swarm of atoms in a Stanford lab has become the coldest stuff on Earth. At about 50 trillionths of a kelvin, the atoms’ temperature was about a tenth of the previous record.

The temperature of a sample depends on how fast its constituent components move relative to each other. Quantum physicist Mark Kasevich and his team started with a cold gas made up of about 100,000 tightly packed rubidium atoms. Within a few seconds, the atoms spread apart, because some were moving faster than others. But then Kasevich’s team zapped the sample with a laser that countered the  motion. The farther an atom had roamed (and thus the faster it was moving), the more of a decelerating nudge it received. All the atoms slowed to a crawl, the researchers report in the April 10 Physical Review Letters, corresponding to the new record-low temperature.

Ultracold atoms should lead to increasingly sensitive interferometers, devices that can measure gravity and test the limits of quantum theory. Kasevich hopes to improve the technique and cool atomic gases to quadrillionths of a kelvin.