A tiny cloud of atoms aboard China’s Tiangong space station reached an equivalent temperature of 9.7 picokelvin, setting a new orbital record for extreme cold, The Brighter Side of News reported.
One picokelvin equals one-trillionth of a kelvin; the 9.7-picokelvin equivalent temperature describes how slowly the atoms spread after their confinement was switched off.
Researchers created the Bose–Einstein condensate using optical dipole traps housed inside the Cold Atom Physics Rack within the Mengtian laboratory module, which launched in October 2022. Xiaoji Zhou, Weibiao Chen, and Xuzong Chen led the collaboration that produced the ultracold cloud containing roughly 20,000 rubidium atoms.
On Earth, gravity pulls atomic clouds downward, limiting how weak optical traps can become before the atoms escape. Orbiting laboratories like Tiangong fall continuously around Earth, creating a microgravity environment that allows much weaker confinement without gravitational sag.
This orbital setting also extends observation windows compared to terrestrial drop towers, which lose their experimental window once the drop distance ends. However, microgravity complicates evaporative cooling because trapped atoms do not tilt naturally against the trap walls. To fix this, the research team applied a magnetic-field gradient during the initial cooling stage to assist selective evaporation.
After lowering the cloud’s energy using crossed-beam optical trap arrangements, researchers switched off the second trap and photographed the expanding gas from two directions. The atoms remained visible after seven seconds of free expansion in orbit.
The research team calculated the three-dimensional equivalent temperature using expansion data captured between 300 and 1,600 milliseconds. A decompression duration of 1.175 seconds yielded the lowest measured expansion energy during the tested sequence.
The 9.7 picokelvin benchmark provides a versatile platform for future orbital quantum-gas mixtures and precision measurements. Shaped laser fields could allow scientists to simulate complicated many-particle systems or test fundamental physics principles using pathfinder atom interferometry.
The authors suggest that increasing atom numbers through adjustable trap volumes could yield further insights. Turning this ultracold source into a working sensor will require additional control sequences and careful management of external disturbances.
Temperature normally measures the statistical distribution of energy in a system. For an expanding quantum gas, researchers measure the cloud’s expansion, calculate the kinetic energy, and express that energy using temperature units.
The Tiangong result of 9.7 picokelvin is roughly one-quarter of a previous 38-picokelvin benchmark achieved in a drop-tower experiment. Earlier work aboard the International Space Station reached an effective temperature of 52 picokelvin using magnetic confinement.
No atoms reached absolute zero during the experiment. Quantum physics makes extreme cooling more subtle than simply stopping all motion, and the measurement reflects the slow expansion rate of a carefully prepared atomic sample.