On the International Space Station, astronauts are weightless. Atoms are, too.
That weightlessness makes it easier to study a weird quantum state of matter known as a Bose-Einstein condensate. Now, the first Bose-Einstein condensates made on the space station are reported in the June 11 Nature.
The ability to study the strange state of matter in orbit will aid scientists’ understanding of fundamental physics as well as make possible new, more sensitive quantum measurements, says Lisa Wörner of the German Aerospace Center Institute of Quantum Technologies in Bremen. “I cannot overstate the importance of this experiment to the community,” she says.
A Bose-Einstein condensate occurs when certain types of atoms are cooled to such low temperatures that they take on one unified state. “It’s as though they’re joining arms and behaving as one harmonious object,” says physicist David Aveline of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. To produce the weird state of matter in orbit, he and colleagues created the Cold Atom Lab, which was installed on the space station in 2018.
In orbit, the atoms are in free fall, continuously plummeting under the force of gravity, producing a weightlessness like that felt by riders when a roller coaster suddenly drops. Those conditions, known as microgravity, make the space station an ideal environment for studying Bose-Einstein condensates.
To make a Bose-Einstein condensate, atoms must be cooled while trapped with magnetic fields. On Earth, the trap must be strong enough to prop the atoms up against gravity. Because that’s not a concern in microgravity, the trap can be weakened, allowing the cloud of atoms to expand and cool. This process allows the condensate to achieve lower temperatures than are possible with the same methods on Earth. In the Cold Atom Lab, rubidium atoms reached tenths of billionths of kelvins.
Bose-Einstein condensates are already the record holders for the lowest known temperatures (SN: 4/13/15). With further improvement to the cooling techniques, scientists expect that the Cold Atom Lab could go even colder, to temperatures below any known in the universe.
Another boon of microgravity is that measurements of the bizarre matter can be made for longer periods of time. Normally, atoms are released from the trap and then imaged quickly before gravity pulls them out of view. But in microgravity, researchers found that they could observe the released atoms for as long as 1.1 seconds. On Earth, the same techniques yield observation times of about 40 milliseconds.
Those longer observation times could allow for more sensitive measurements. The atoms could be used to detect forces, including how Earth’s gravity varies over time and across different parts of the planet. Future experiments on dedicated satellites could make new, more sensitive measurements of phenomena such as sea level rise.
And the quantum matter could also be used to test fundamental principles of physics, such as Einstein’s equivalence principle (SN: 12/4/17). That’s the idea that objects of different masses or compositions — or in this case, different types of atoms — will fall due to gravity at the same rate.
Previous experiments have studied Bose-Einstein condensates on a rocket shot into space that quickly fell back to Earth and in a tower that launched an apparatus upward and let it fall back down. But the short duration of such flights limits how many experiments can be performed.
“This is of course the big advantage” of the space station, says physicist Maike Lachmann of Leibniz University Hannover in Germany, who coauthored a perspective article that appears in the same issue of Nature. With about two years already logged on the space station, the Cold Atom Lab has already had plenty of time for experiments. “They can do very, very exciting things,” Lachmann says.