On a sun-drenched hill in Southern California’s San Gabriel Mountains, researchers from NASA’s Jet Propulsion Laboratory in Pasadena are making progress on an experimental facility that could create the coldest known place in the universe. It’s called the Cold Atom Laboratory (CAL) and is expected to probe the wonders of quantum physics when it launches to the International Space Station in August 2017.
CAL researchers are interested in a state of matter called a Bose-Einstein condensate, which happens when all the atoms in a very cold gas have the same energy levels. Like dancers in a chorus line, the atoms become synchronized and behave like one continuous wave instead of discrete particles.
“Studying gases that have been cooled down to extreme temperatures is key to understanding how complexity arises in the universe, and allows us to test the fundamental laws of physics in a whole new way,” says Robert Thompson, a project scientist at CAL.
On Earth, gravity limits how long scientists can study Bose-Einstein condensates because this form of matter falls to the bottom of any apparatus used to study it. In microgravity, such condensates can be observed for longer periods of time, allowing scientists to better understand the properties of particles in this state and their uses for tests of fundamental physics. Ultracold atoms in microgravity may also be key to a wide variety of advanced quantum sensors and exquisitely sensitive measurements of quantities such as gravity, rotations and magnetic fields.
Using lasers, magnetic traps and an electromagnetic “knife” to remove warm particles, CAL will take atoms down to the coldest temperatures ever achieved. In February, the team created its first ultracold quantum gas made from two elemental species, rubidium and potassium. In 2014, CAL researchers had previously made Bose-Einstein condensates using rubidium and were able to reliably create them in a matter of seconds. This time, the cooled rubidium was used to cool potassium-39 down to about a millionth of a degree Kelvin above absolute zero, the point at which its atoms would be close to motionless.
Once installed at ISS, researchers hope to cool atoms down to a billionth of a degree above absolute zero. “This marks an important step for the project, as we needed to verify that the instrument could create this two-species ultracold gas on Earth before doing so in space,” says Anita Sengupta, the project manager for CAL.
CAL is also expected to contribute to Efimov physics, a field that makes predictions about how a small number of particles interact. Isaac Newton had fundamental insights into how two bodies interact—for example, Earth and the moon—but the rules that govern them are more complicated when a third body, such as the sun, is introduced. The interactions become even more complex in a system of three atoms, which behave according to the odd laws of quantum mechanics.
Under the right conditions, the ultracold gases that CAL produces contain molecules with three atoms each and are a thousand times bigger than a typical molecule. This results in a low-density, “fluffy” molecule that quickly falls apart unless it is kept extremely cold. “The way atoms behave in this state gets very complex, surprising and counterintuitive, and that’s why we’re doing this,” says Eric Cornell, a physicist at the University of Colorado and the National Institute of Standards and Technology, both in Boulder, and member of the CAL science team. Cornell shared the 2001 Nobel Prize in physics for creating Bose-Einstein condensates.
At a recent meeting at JPL, researchers associated with the mission gathered to discuss ongoing developments and scientific goals that ranged from dark matter detection to atom lasers. The group included Cornell, who, along with co-investigator Peter Engels of Washington State University, is leading one of the CAL experiments. “CAL science investigators could open new doors into the quantum world and will demonstrate new technologies for future NASA missions,” said CAL Deputy Project Manager Kamal Oudrhiri at JPL.