China space station sets new record, cools atoms to 9.7 picokelvin, could help new experiments

A cloud of rubidium atoms was tracked for seven seconds after researchers released it from a laser trap aboard China’s space station.

By tracking that motion in three dimensions, the team measured a record-low equivalent temperature of 9.7 picokelvin, about a quarter of the previous record.

The experiment used microgravity to produce and manipulate a Bose–Einstein condensate, a state in which atoms behave collectively as a single quantum wave.

The ability to watch the cloud expand for several seconds could give researchers more time to probe unusual states of matter and make precision measurements in orbit.

Why the team went to orbit

On Earth, gravity pulls atoms downward inside a trap, making them harder to hold as the confinement weakens.

Researchers can counter that pull with magnetic levitation, but doing so requires the atoms to share the same internal spin state. A trap made from focused laser beams gives researchers more flexibility over those states.

Earlier experiments found ways to give atoms a brief period of free fall. A drop tower produced the previous record of 38 picokelvin and gave researchers two seconds to observe the cloud’s expansion.

The International Space Station’s Cold Atom Laboratory reached 52 picokelvin using magnetic trapping and matter-wave lensing, with one second of free expansion.

The orbital setup gave the team a longer period of microgravity than a ground-based drop tower could provide.

A laser trap slows the cloud

The team started with around 20,000 rubidium atoms. Laser cooling slowed the atoms, and evaporative cooling removed the most energetic ones, allowing the remaining atoms to form a condensate inside an optical dipole trap.

A magnetic-field gradient aided the initial cooling and helped produce a condensate that was less sensitive to magnetic disturbances.

The researchers then moved the cloud into a wider optical trap and gradually loosened its grip. This step reduced the energy driving the cloud’s expansion after release.

The team tracked how quickly it grew along three axes and used that motion to calculate an equivalent temperature, a measure of the energy associated with the expansion. The uncertainty around the 9.7-picokelvin estimate ranged from 7.0 to 12.9 picokelvin.

What the longer window could enable

The authors describe Bose–Einstein condensates as “versatile platforms for quantum simulation.”

In orbit, they could use precisely shaped laser fields to examine how quantum order decays in a gas confined to one dimension or how atoms organize in a disordered environment.

The team said traps with adjustable volumes could also accommodate more atoms in future experiments.

Another possibility is an instrument that splits and recombines atomic waves to detect small differences in motion. The longer observation window could give those differences more time to build up, making them easier to measure.

“A second possible objective is the construction of a space-based atom Mach-Zehnder interferometer, with the potential to perform precision tests of fundamental principles, such as the equivalence principle,” the authors wrote.

One such test would examine whether different objects fall with the same acceleration under gravity. An orbital instrument would use the behavior of atomic waves to probe that principle.

The study was published in the Science journal.