Physicists aboard China’s Tiangong space station achieved a record equivalent temperature of just 9.7 picokelvins, dropping the threshold four times lower than a 2021 drop-tower benchmark, ScienceAlert reported.
Absolute zero sits at zero kelvins as a theoretical lower limit where thermal energy cannot plunge any lower, according to ScienceAlert. The universe’s background temperature hovers around 2.7 kelvins.
Researchers Xiaoji Zhou and Xuzong Chen of Peking University led the team alongside Weibiao Chen of the Chinese Academy of Sciences. They published their findings in the journal Science.
The experiment began with a cloud of roughly 20,000 rubidium-87 atoms. Lasers confined and cooled the atoms aboard the Tiangong station, as reported by ScienceAlert.
Evaporative cooling removed the most energetic atoms from the trap. Because continuous orbital free fall lacked gravity’s natural assistance in pulling escaping atoms away, researchers applied a magnetic-field gradient during cooling, according to ScienceAlert and Interesting Engineering.
New Atlas noted that the team transferred the remaining slow atoms into a wider optical trap. They reduced its strength before releasing the cloud entirely.
The team tracked how quickly the atomic cloud grew along three axes after release, Interesting Engineering reported. The cloud remained detectable for seven seconds.
By measuring that expansion rate, the team calculated an equivalent temperature ranging between 7.0 and 12.9 picokelvins, with a central estimate of 9.7 picokelvins, according to Interesting Engineering.
This metric measures the energy tied to the cloud’s slow expansion rather than providing a conventional thermometer reading, ScienceAlert explained.
NASA previously created a Bose-Einstein condensate on the International Space Station in 2018, cooling rubidium atoms to 100 nanokelvins, ScienceAlert reported. A subsequent 2021 drop-tower experiment in Germany reached 38 picokelvin during two seconds of free fall, according to Interesting Engineering.
Earth’s gravity pulls atoms downward against a trap as confinement weakens. Orbital flight provides extended microgravity, allowing longer observation windows than ground-based towers manage, Interesting Engineering noted.
Longer observation windows give atomic waves more time to develop measurable differences, opening paths for space-based atom interferometers, according to Interesting Engineering.
It is an exotic state of matter that forms when certain atoms cool to fractions of a degree above absolute zero. At these extremes, atoms occupy the same quantum state and behave collectively as a single quantum wave, as reported by New Atlas.
Rubidium atoms are used in space experiments involving laser cooling and the creation of Bose-Einstein condensates. Researchers use it to study quantum behavior on larger scales.
It describes the energy associated with an atomic cloud’s expansion after release. Scientists observe how slowly the atoms move to determine their energy level, expressing that motion in kelvins, ScienceAlert stated.
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