BEIJING, Nov. 6 (Xinhua) -- Chinese scientists have set a new record for the coldest temperature ever achieved by humans, cooling a cloud of rubidium atoms to 9.7 picokelvin, and keeping it stable for observation for seven seconds.
The result, announced at a briefing on China's space station program by the Chinese Academy of Sciences (CAS), marks a major step toward absolute zero, the lowest temperature theoretically possible, creating the coldest artificial substance known to date. The work was published on Friday in the journal Science.
The experiment was carried out in the ultra-cold atom physics rack aboard China's space station. The project began feasibility studies in 2011, and its experiment system was launched with the Mengtian module in 2022. It was organized by the Technology and Engineering Center for Space Utilization under the CAS, while completed by Peking University and the Shanghai Institute of Optics and Fine Mechanics (SIOM) of the CAS.
"This is the result of close collaboration between the overall system, the science team and the engineering team," said Wang Qiang, chief commander of the space application system of China's manned space program.
Atoms are always in random thermal motion, and cooling them means slowing them down. Only near absolute zero, approximately minus 273.15 degrees Celsius, do atoms become almost still, forming orderly quantum states that scientists can study. Reaching that point has been a century-old challenge in physics. The previous record was 38 picokelvin, set by a German team in 2021.
The Chinese team used an all-optical trap to hold the atom cloud, then lowered the laser intensity to cool it further through evaporation, and finally applied a deep-cooling step called non-adiabatic diffusion. Compared with the magnetic-trap approach used internationally, the Chinese method is harder to implement but offers clear advantages: it is less sensitive to magnetic interference, easier to control precisely in space, and has more available optical accesses. Consequently, it is compatible with a wider range of quantum simulation experiments. Under microgravity, atoms can be held with much weaker confinement, allowing lower temperatures and longer observation times.
To achieve such a target, the team integrated a ground-based experimental system of around 20 cubic meters and 10 tonnes into a rack of just 0.7 cubic meters and 0.5 tonnes, overcoming key challenges in ultra-high vacuum systems, high-power fiber lasers, long-term laser frequency stabilization and high-precision optical integration.
"The engineering challenge was to concentrate multiple cutting-edge technologies under strict aerospace requirements," said Li Tang, a researcher at SIOM.
Cooling atoms to near absolute zero stretches their de Broglie wavelengths to observable scales, making quantum effects more visible and controllable. This provides a clean, flexible platform for quantum simulation and supports technologies such as high-precision atomic clocks, atom-interferometry inertial measurement and quantum computing. Longer observation times matter -- ground experiments can watch atoms for only about 0.05 seconds, the International Space Station for roughly 1 second, and China's space station now for 7 seconds.
"The longer we can observe, the more likely we are to find new and fainter physical phenomena," said Xiong Wei, a co-first author of the paper.
This achievement could help scientists study phase transitions, non-equilibrium dynamics and quantum many-body correlations at extremely low temperatures, and support research into early-universe simulation and ultralight dark matter detection, said Chen Weibiao, a researcher at SIOM.
Lyu Congmin, chief designer of the space application system of China's manned space program, said: "We welcome scientists from all over the world to conduct experimental research with the ultra-cold atom physics rack on the Chinese space station to make new contributions to the scientific community." ■
