Physicists at Caltech and the Jet Propulsion Laboratory have created a rare quantum state of matter known as a Bose-Einstein condensate (BEC) in space for the first time, according to a recent paper published in the journal Nature. The physicists did so by placing a compact experimental setup the size of a mini-fridge on board the International Space Station (ISS). It’s called the Cold Atom Laboratory (CAL), aka “the coolest spot in the universe.”
BECs are named in honor of Albert Einstein and Indian physicist Satyendra Bose, who predicted the possibility in the 1920s that the wavelike nature of atoms might allow the atoms to spread out and overlap if they are packed closely enough together. At normal temperatures, atoms act like billiard balls, bouncing off one another. Lowering the temperature reduces their speed. If the temperature gets low enough (billionths of a degree above absolute zero) and the atoms are densely packed enough, the different matter waves will be able to “sense” one another and coordinate themselves as if they were one big “superatom.”
Physicists Eric Cornell and Carl Wieman, then at the University of Colorado’s JILA facility, created the first BECs in the laboratory in 1995. Using a laser trap, they cooled about 10 million rubidium gas atoms; the cooled atoms were held in place by a magnetic field. But the atoms still weren’t cold enough to form a BEC, so they added a second step, evaporative cooling, in which a web of magnetic fields conspire to kick out the hottest atoms so that the cooler atoms can move more closely together. The process works in much the same way that evaporative cooling occurs with your morning cup of coffee; the hotter atoms rise to the top of the magnetic trap and “jump out” as steam.
By September 2001, over three dozen teams had replicated the experiment. The discovery launched an entirely new branch of physics. BECs enable scientists to study the strange, small world of quantum physics as if they were looking at it through a magnifying glass; a BEC “amplifies” atoms in the same way that lasers amplify photons. Wieman, Cornell, and Wolfgang Ketterle shared the 2001 Nobel Prize in Physics for their achievement.
While the laboratory equipment required to make a BEC on Earth can easily fill a room, JPL’s miniaturized CAL is just 14 cubic feet and only needs about 510 watts to operate, making it ideal for ISS microgravity experiments. CAL was installed on board in May 2018. Right now the setup uses rubidium atoms to make the BECs, but there are plans to incorporate potassium atoms into the mix to explore the physics of mixed BECs.
It’s a significant achievement because BECs created in space last longer than they do in terrestrial laboratories once the confining traps are switched off, giving physicists a bit more time to study the exotic state of matter—over one second, compared to mere fractions of a second on Earth. As Neel Patel explains at Technology Review:
To run experiments using a BEC, you need to turn down or release the magnetic trap. The cloud of crowded atoms will expand, which is useful because BECs need to stay cold, and gases tend to cool off as they expand. But if the atoms in a BEC get too far apart, they no longer behave like a condensate. This is where the microgravity of low Earth orbit comes into play. If you try to increase the volume on Earth, says [JPL physicist David Aveline, a co-author of the recent paper in Nature], gravity will just pull the atoms in the center of the BEC cloud down to the bottom of the trap until they spill out, distorting the condensate or ruining it entirely.
But in microgravity, the tools in the CAL can hold the atoms together even as the trap’s volume increases. That makes for a longer-lived condensate, which in turn allows scientists to study it longer than they could on Earth (this initial demonstration ran for 1.118 seconds, although the goal is to be able to detect the cloud for up to 10 seconds).
“We’re getting to make BECs on a daily basis, for many hours a day,” Aveline told Business Insider. “CAL is completely remote-controlled. We’re running it from computers on the ground, literally inside our living rooms.”
CAL was originally supposed to last for a year or so before requiring replacement parts, but the ISS astronauts—notably Christina Koch—have been performing crucial maintenance to extend its lifetime. CAL has been operating for a full two years now. Among the recent enhancements is an atom interferometer, which can use the BECs to measure any changes in gravity on a planetary surface. BECs might also eventually be able to detect axions, a theoretical cold dark matter particle, or be used to hunt for sources of dark energy.
“In the past, our major insights into the inner workings of nature have come from particle accelerators and astronomical observatories,” co-author Robert Thompson of Caltech told Space.com. “In the future, I believe precision measurements using cold atoms will play an increasingly important role.”