Enlarge /. This series of false-color images shows the formation of a Bose-Einstein condensate in the prototype of the Cold Atom Laboratory in NASA's Jet Propulsion Laboratory when the temperature approaches absolute zero, the temperature at which atoms have almost no movement.
The physicists from Caltech and the Jet Propulsion Laboratory have, for the first time, created a rare quantum state of matter known as Bose-Einstein condensate (BEC) in space, according to a recent article in Nature magazine. For this purpose, the physicists placed a compact experimental setup the size of a mini fridge on board the International Space Station (ISS). It's called Cold Atom Laboratory (CAL), also known as "the coolest place in the universe".
BECs are named in honor of Albert Einstein and Indian physicist Satyendra Bose, who predicted in the 1920s the possibility that the wavy nature of atoms could allow atoms to spread and overlap when packed closely enough. At normal temperatures, atoms act like billiard balls and bounce off each other. Lowering the temperature reduces the speed. When the temperature becomes low enough (billionths of a degree above absolute zero) and the atoms are packed close enough, the various matter waves can "grasp" and coordinate with each other as if they were a large "super atom".
The physicists Eric Cornell and Carl Wieman, then at the JILA facility at the University of Colorado, created the first BECs in the laboratory in 1995. With a laser trap, they cooled about 10 million rubidium gas atoms. The cooled atoms were held in place by a magnetic field. However, the atoms were still not cold enough to form a BEC, and added a second step, evaporative cooling, which combines a network of magnetic fields to drive out the hottest atoms so that the cooler atoms can move closer together . The process works similarly to evaporative cooling 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 repeated the experiment. The discovery opened up a completely new branch of physics. With BECs, scientists can examine 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 received the 2001 Nobel Prize in Physics for their achievements.
The Cold Atom Laboratory consists of two standardized containers that were installed on the International Space Station in May 2018.
NASA / JPL-Caltech
David Aveline observes CAL at NASA's Jet Propulsion Lab before launch.
NASA / JPL-Caltech
NASA astronaut and flight engineer for Expedition 61, Christina Koch, works at the Cold Atom Lab and swaps and cleans hardware in the quantum research device.
While the laboratory equipment needed to manufacture a BEC on Earth can easily fill a space, JPL's miniaturized CAL is only 14 cubic feet in size and requires only about 510 watts to operate, making it ideal for ISS microgravity experiments. CAL was installed on board in May 2018. Rubidium atoms are currently used in the manufacture of the BECs. However, it is planned to include potassium atoms in the mixture to study the physics of mixed BECs.
This is a significant achievement because BECs created in space last longer after the boundary traps are turned off than in terrestrial laboratories. This gives physicists a little more time to study the exotic state of matter – over a second compared to fractions of a second on Earth. As Neel Patel explains at Technology Review:
To perform experiments with a BEC, you must turn down the magnet trap or release it. The cloud of crowded atoms will expand, which is useful because BECs need to stay cold and gases tend to cool as they expand. However, if the atoms in a BEC are too far apart, they will no longer behave like condensate. This is where the microgravity of Earth's orbit comes into play. When you try to increase the volume on Earth, says gravity (JPL physicist David Aveline, co-author of the recent article in Nature), gravity simply pulls the atoms in the middle of the BEC cloud to the bottom of the trap, until you leak, distort the condensate, or ruin it completely.
In microgravity, the tools in the CAL can hold the atoms together even if the volume of the trap increases. This results in a longer-lasting condensate, which in turn enables scientists to study it longer than on Earth (this first demonstration lasted 1.118 seconds, although the goal is to be able to see the cloud for up to 10 seconds).
"We will produce BECs many hours a day," Aveline told Business Insider. "CAL is completely remote controlled. We run it from computers on the floor, literally in our living rooms."
CAL was originally supposed to take about a year before spare parts were needed, but the ISS astronauts – especially Christina Koch – did important maintenance to extend their lifespan. CAL has been in operation for two years. Recent improvements include an atomic interferometer that uses BECs to measure changes in gravity on a planet's surface. BECs could also potentially detect axions, a theoretical particle made of cold dark matter, or be used to search for sources of dark energy.
"In the past, particle accelerators and astronomical observatories have given us our most important insight into the inner workings of nature," Caltech co-author Robert Thompson told Space.com. "I believe that precision measurements with cold atoms will play an increasingly important role in the future."
DOI: Nature, 2020. 10.1038 / s41586-020-2346-1 (About DOIs).