China’s space station chilled atoms to 9.7 picokelvin, the coldest on record

A cloud of rubidium atoms aboard China’s Tiangong space station has been chilled to less than ten trillionths of a degree above absolute zero, the coldest temperature ever reported for a gas of atoms. That is roughly four times colder than the best result achieved anywhere before, on Earth or in orbit.

The record matters less for the number than for what it buys. At that chill, the atoms drift apart so slowly that the team could watch the cloud for seven seconds after letting it go, a window long enough to test gravity, quantum behaviour and possibly dark matter with a precision no ground lab can reach.

The atoms formed a Bose-Einstein condensate, a state of matter in which thousands of atoms lose their individuality and behave as a single quantum wave. Researchers from Peking University, the Shanghai Institute of Optics and Fine Mechanics and the Chinese Academy of Sciences’ Technology and Engineering Center for Space Utilization ran the experiment in the cold atom physics rack of the station’s Mengtian laboratory module, and reported it in the journal Science.

The cloud held 20,000 atoms of rubidium-87. Its equivalent temperature came out at 9.7 picokelvin, with an uncertainty running from 7.0 to 12.9 picokelvin. The previous lowest figure for such a system was 38 picokelvin, and NASA’s Cold Atom Lab on the International Space Station had reached 52.

How a ten-tonne lab was squeezed into a station rack

Cooling atoms means slowing them down. The team trapped the rubidium with crossed laser beams, an arrangement called an optical dipole trap, then lowered the laser power step by step so the most energetic atoms could escape. This is evaporative cooling, the same principle that cools a cup of coffee when the hottest molecules leave as steam.

In microgravity that trick works less well, because the atoms no longer settle toward the bottom of the trap where the escape route is. The researchers added a weak magnetic gradient to steer the evaporation and get a condensate. A final stage, a sudden non-adiabatic expansion of the trap, then slowed the atoms further.

Every other record of this kind used magnetic traps built on atom chips. Lasers are harder to run in orbit, but they are less sensitive to magnetic interference, leave more room for optical access and can hold atoms that ignore magnetic fields altogether. “The engineering challenge was to concentrate multiple cutting-edge technologies under strict aerospace requirements,” said Li Tang, a researcher at the Shanghai institute, according to Xinhua.

The ground version of the experiment fills about 20 cubic metres and weighs around 10 tonnes. The flight rack occupies 0.7 cubic metres and half a tonne, with its ultra-high vacuum system, high-power fibre lasers and frequency-stabilised optics running automatically, under tight power limits.

Hundreds of billions of times colder than deep space

Absolute zero, minus 273.15 degrees Celsius, is the point where atomic motion would stop entirely. Empty space is not that cold: the faint afterglow of the Big Bang keeps it at about 2.7 degrees above absolute zero. Measured on the kelvin scale, the Tiangong cloud was about 280 billion times colder than that.

The previous best, 38 picokelvin, came from a German team that dropped an atom-chip experiment down the Bremen drop tower to get a few seconds of weightlessness. Drop towers run out of height. An orbiting station is in permanent free fall, so the experiment can keep going for as long as the atoms stay coherent.

Observation time is where the gap widens most. Ground experiments can follow a released cloud for about 0.05 seconds before it falls out of view, the International Space Station manages roughly one second, and the Chinese station now reaches seven, according to the team. “On Earth, it would fall down by about 250 meters, so it would actually crash to the ground unless you have a vacuum chamber, which is 250 meters high,” said Wolfgang Ketterle, the MIT physicist who shared the Nobel Prize for creating Bose-Einstein condensates, speaking to China’s CGTN.

What equivalent temperature does and does not mean

The 9.7 picokelvin is not a thermometer reading. Researchers infer it from how slowly the cloud spreads after release, converting that expansion speed into the temperature a gas would need to move that slowly. The figure describes the atoms alone: the researchers point out that the equipment and its surroundings never came close to that temperature.

The error bar is wide, roughly 30 percent either side, and the result comes from a single facility and has not yet been reproduced independently. Comparisons with older records also mix methods: drop towers, magnetic chips and now laser traps reach their numbers through different trapping and final cooling methods, so the gap is a guide, not a precise ranking.

The cloud is also small. Twenty thousand atoms is enough for a clean condensate, but precision instruments gain sensitivity from larger samples. Whether the system can deliver both more atoms and long coherence on a routine basis is the open engineering question.

Why seven seconds matter more than the record

An atom interferometer splits each atom’s quantum wave into two paths and recombines them, turning tiny differences in acceleration into a measurable signal. Its sensitivity grows with the square of the time the atoms spend inside it. “Atom interferometers highly benefit from sources providing a large number of atoms in an ultracold ensemble and long observation times,” said Ernst Rasel, a physicist at Leibniz University Hannover, in comments carried by CGTN.

Such instruments could map Earth’s gravity field from orbit and test whether objects of different composition really fall at the same rate, a cornerstone of Einstein’s relativity. Laser traps can also be shaped into optical lattices, grids of light that hold atoms like a crystal and let physicists simulate materials that are hard to study directly. “The longer we can observe, the more likely we are to find new and fainter physical phenomena,” said Xiong Wei of Peking University, co-first author of the paper, according to Xinhua.

Common questions about the coldest temperature ever recorded

What is the coldest temperature ever recorded?

For a gas of atoms, the lowest equivalent temperature reported so far is 9.7 picokelvin, reached aboard China’s Tiangong space station. That is 9.7 trillionths of a degree above absolute zero. The previous record was 38 picokelvin.

What is a Bose-Einstein condensate?

It is a state of matter that forms when a gas of certain atoms is cooled close to absolute zero. The atoms fall into the same quantum state and act as one wave, which makes quantum effects visible on a scale large enough to photograph.

Why do cold atom experiments work better in space?

On Earth, gravity pulls the atoms out of weak traps and makes a released cloud fall within a fraction of a second. In orbit, the atoms float, so the trap can be made gentler, which cools them further, and the cloud can be watched for several seconds.

Can anything reach absolute zero?

No. The laws of thermodynamics forbid reaching exactly zero kelvin, so experiments can only get ever closer. Each step down becomes harder, which is why going from 38 to under 10 picokelvin counts as a large jump.

An orbiting lab open to outside teams

The cold atom rack went up with the Mengtian module in 2022, after a project whose first feasibility studies began in 2011, and the record was published online in Science on November 5, 2026. Rasel sees the next step as interferometers in orbit that keep atoms coherently split for several seconds. Lyu Congmin, chief designer of the space application system of China’s crewed space programme, said the rack is open to scientists from all over the world who want to run their own experiments on it.

Reference: Xiong et al., “Quantum gases below 10 picokelvin in space,” Science, 2026. DOI: 10.1126/science.aea5324

Tags: physics, quantum physics, absolute zero, Bose-Einstein condensate, Chinese Academy of Sciences, Mengtian