Tiangong experiment measures atomic cloud at 9.7 picokelvin

Researchers aboard China's Tiangong space station achieved an equivalent temperature of 9.7 picokelvin in an atomic cloud, Phys.org reports, citing research published in Science. The measurement has an uncertainty range of 7.0 to 12.9 picokelvin. The team used laser and evaporative cooling to form a shared quantum state from around 20,000 rubidium atoms, then weakened a wider optical trap to reduce the cloud's expansion energy. They tracked its free expansion for 7 seconds, compared with 2 seconds in a previous drop-tower experiment. The result expands experimental capacity for quantum physics in microgravity. Equivalent temperature describes the cloud's expansion energy and velocity rather than an ordinary thermodynamic temperature.