Tiangong space station: rubidium atoms cooled to 10 picokelvins, a record-low temperature

Scientists have cooled a cloud of atoms to about 10 picokelvins, or 10 trillionths of a kelvin, producing a Bose-Einstein condensate colder than any before, according to Science News. The researchers reported the result on November 5 in Science. The experiment ran aboard China's Tiangong space station in Earth orbit. The temperature is barely above absolute zero, −273.15° Celsius sciencenews.orgScience Newssciencenews.orgOpen source ↗.

How the atoms were cooled

Researchers used laser-based traps to contain 20,000 rubidium atoms and reduce their motion, which cooled them sciencenews.orgScience Newssciencenews.orgOpen source ↗. At the atomic level, temperature is tied to motion: atoms and molecules in the air around us move more slowly when it is colder. In systems of cold atoms, scientists define an effective temperature from how slowly the atoms spread apart when they are allowed to expand.

On Earth, gravity makes clouds of atoms sag, which reduces the effectiveness of cooling. On the station the atoms experienced microgravity, the apparent weightlessness of an object in free fall sciencenews.orgScience Newssciencenews.orgOpen source ↗. To make a Bose-Einstein condensate, a disordered group of atoms is cooled until all of them take the same quantum state and act as one entity.

Earlier records and uses

Bose-Einstein condensates were previously made on the International Space Station, at effective temperatures as low as 52 picokelvins. An experiment on Earth, in which atoms were dropped down a tower to induce weightlessness, reached 38 picokelvins sciencenews.orgScience Newssciencenews.orgOpen source ↗. Drop tower experiments are limited by the duration of the free fall, which is not a constraint for experiments in Earth orbit.

Ultracold atoms let researchers study exotic states of matter and other physical phenomena. They can also be used to test fundamental concepts, such as the equivalence principle, the idea that explains why objects of different masses fall at the same rate in a vacuum sciencenews.orgScience Newssciencenews.orgOpen source ↗.