Scientists aboard China's Tiangong space station have cooled a cloud of atoms to 10 picokelvins, just above absolute zero and the coldest temperature ever recorded, using a laser trap in orbit, Live Science reported.
Absolute zero is minus 459.67 degrees Fahrenheit (minus 273.15 degrees Celsius), the theoretical point at which particles in an object are believed to stop moving. A picokelvin is a trillionth of a kelvin, so 10 picokelvins is a vanishingly small step above that floor. The team reported the result Nov. 5 in the journal Science.
The researchers used what are commonly called optical tweezers, more formally an optical-dipole trap, which hold atoms in a laser beam. They placed 20,000 rubidium atoms in the trap to restrict their motion. That reduced movement, combined with the weightlessness of the station's low-gravity environment, allowed the cloud to cool far below temperatures that are practical on Earth, the scientists said.
"This record-low temperature could stimulate a new generation of ODT-based experiments in quantum simulation and precision measurements in space," the researchers wrote in the paper, according to Live Science. In other words, the point of the experiment is not only to post a temperature record, but to show that a space-based laser trap can prepare ultracold atoms for later tests of quantum physics and ultra-precise measurement.
Hitting absolute zero itself remains out of reach. Live Science noted that one interpretation of the third law of thermodynamics says it cannot be attained. The Tiangong result is valuable because it gets extraordinarily close under conditions — microgravity and a carefully controlled optical trap — that Earth-bound labs struggle to match for the same number of atoms.
Ultracold atom experiments on Earth already underpin some of the world's best clocks and tests of fundamental physics. Doing the same work in orbit, where gravity does not pull the cloud apart in the same way, could extend the time atoms remain usefully cold and confined. The paper frames 10 picokelvins as a starting point for that line of work, not a final destination.
The achievement is also a marker of how much experimental physics is now being done on Tiangong. A record temperature in a 20,000-atom rubidium cloud will not change daily life, but it sets a benchmark other labs, on the ground and in space, will try to meet or beat, and it gives Chinese researchers a published foothold in a field that has long been led by groups in the United States and Europe.