Chinese scientists have achieved a record-low equivalent temperature of 9.7 picokelvins in an experiment aboard the Tiangong space station. The achievement, reported November 5 in the journal Science, involved cooling approximately 20,000 rubidium atoms to an extraordinary level just above absolute zero.
The experiment took place inside the station's Mengtian laboratory module, where researchers used specialized laser equipment to control an extremely cold cloud of atoms. The result was approximately four times lower than the previous reported record for comparable experiments.
Scientists also observed the atomic cloud expanding for seven seconds, giving them an unusually long opportunity to study its behavior. The findings could help researchers develop more sensitive instruments for measuring gravity, motion and other physical properties.
How Close Did Scientists Get to Absolute Zero?
Absolute zero is the lowest possible temperature on the thermodynamic scale, equal to minus 273.15 degrees Celsius or minus 459.67 degrees Fahrenheit.
At ordinary temperatures, atoms and molecules move continuously, carrying energy associated with their motion. Cooling reduces that thermal energy.
However, reaching absolute zero does not mean that all atomic motion would completely disappear. Quantum mechanics allows particles to retain a minimum amount of motion even in their lowest energy state.
The Chinese experiment produced an equivalent temperature of 9.7 trillionths of a kelvin above absolute zero.
A picokelvin is one trillionth of a kelvin. The measurement therefore represents an extraordinarily small amount of energy associated with the movement of the atoms.
There is an important distinction in how researchers obtained this figure. The temperature describes the slow expansion of a specially prepared atomic cloud rather than the temperature of the space station or its surroundings.
Scientists calculated the equivalent temperature from the cloud's expansion in three dimensions.
The researchers reported an uncertainty range extending from approximately 7.0 to 12.9 picokelvins. This means 9.7 picokelvins is the central reported value rather than an exact measurement without uncertainty.
Researchers Used Lasers to Cool Thousands of Atoms
The experiment involved scientists from Peking University, the Chinese Academy of Sciences and Fudan University.
Their research, titled Quantum gases below 10 picokelvin in space, describes how the team created an extremely cold state of matter known as a Bose-Einstein condensate.
This unusual state forms when certain atoms become cold enough that their quantum behavior begins to overlap. Instead of behaving independently, the atoms act collectively in ways that scientists can observe and measure.
The researchers began with approximately 20,000 rubidium atoms. Rubidium is commonly used in ultracold physics experiments because its properties make it suitable for controlled cooling and trapping.
According to reporting published by Phys.org, the team combined laser cooling with evaporative cooling to prepare the atoms.
Laser cooling uses carefully controlled light to reduce atomic motion. Evaporative cooling removes higher-energy atoms from a trapped cloud, leaving the remaining particles with less average energy.
The researchers held the atoms inside an optical dipole trap, which uses focused laser beams to confine particles.
After forming the condensate, they transferred the atoms into a wider optical trap. By gradually weakening its confinement, they further reduced the energy associated with the cloud's expansion.
The team then released the atoms and measured how slowly they spread.
The result established a new reported low for the equivalent temperature of an ultracold quantum gas.
Why Microgravity Made the Experiment Possible
Conducting the experiment aboard Tiangong offered an important advantage over laboratories on Earth.
Under normal gravity, an atomic cloud falls when released from its trap. Scientists must either keep it confined or use specialized facilities that provide brief periods of weightlessness.
Researchers have previously used drop towers to create short intervals of microgravity for experiments.
Space stations offer a different environment. Because the station and its contents are in continuous free fall around Earth, scientists can study freely expanding atomic clouds for longer periods.
This extended observation time becomes especially important when the atoms are moving extremely slowly.
In the new experiment, researchers tracked the cloud for seven seconds after release.
The previous benchmark described in the study involved an equivalent temperature of 38 picokelvins and an expansion period of two seconds.
Experiments aboard NASA's Cold Atom Laboratory on the International Space Station have also demonstrated the value of microgravity for studying unusual quantum states.
The Chinese team's measurements demonstrate how a longer observation window can support experiments involving exceptionally low atomic energies.
What the Record Means for Quantum Physics
The findings could improve scientists' ability to study fundamental physical laws.
At extremely low temperatures, quantum effects become easier to observe because thermal motion is greatly reduced.
One possible application involves atom interferometry, a measurement technique that uses the wave-like behavior of atoms.
Researchers can divide and recombine atomic waves to detect extremely small changes in gravity, acceleration and other physical quantities.
Instruments based on these principles could eventually support more sensitive gravitational measurements from space.
Such measurements may help scientists investigate Earth's gravity field, monitor changes in mass distribution or test predictions of fundamental physics.
The technology could also contribute to quantum simulation, in which carefully controlled atoms reproduce physical behavior that is difficult to calculate using conventional methods.
However, these applications remain possibilities rather than demonstrated outcomes of the Tiangong experiment.
The researchers established a new cooling benchmark and observed the resulting atomic cloud. They did not demonstrate a new quantum computer, operational gravitational sensor or other commercial technology.
The achievement primarily advances the experimental methods needed for future research.
Independent Scientists Recognize the Achievement
The findings have attracted attention from physicists working on similar experiments.
Science News reported that the Chinese researchers created the coldest Bose-Einstein condensate yet measured using the reported equivalent-temperature benchmark.
Nick Bigelow, a physicist at the University of Rochester who has worked on NASA's ultracold atom research, praised the results.
He also acknowledged that other research teams are working toward similar temperatures.
The scientific importance extends beyond setting a numerical record. Scientists need both exceptionally cold atoms and enough time to measure their behavior accurately.
Combining these conditions allows researchers to investigate physical effects that might otherwise be too small or too brief to observe.
The experiment also demonstrated the usefulness of optical traps under microgravity conditions, expanding the techniques available for future space-based quantum research.
Tiangong Becomes a Platform for Advanced Physics
China's Tiangong space station provides laboratories for scientific experiments that benefit from long periods of microgravity.
The Mengtian module contains specialized equipment for conducting research in several fields, including ultracold atomic physics.
The new experiment used the station's Cold Atom Physics Rack, developed to support the preparation and measurement of extremely cold atomic samples.
The result provides a foundation for further studies involving quantum gases and precision measurement systems.
Scientists may use similar methods to increase the number of atoms available for experiments or investigate other forms of quantum matter.
Researchers will also need to determine how reliably the method can reproduce such low equivalent temperatures and whether the approach can support practical measurement instruments.
For now, the verified achievement is a cloud of approximately 20,000 rubidium atoms with an equivalent temperature of 9.7 picokelvins and an observation period of seven seconds.
Those measurements establish a new benchmark for experiments studying quantum matter in space.