Realizing an ultracold bubble—potentially Bose-Einstein condensed—relates to areas of interest, including quantized-vortex flow constrained to a closed surface topology, collective modes, and self-interference via bubble expansion. Using a radiofrequency-dressing protocol, scientists created bubbles of ultracold atoms in NASA‘s Cold Atom Lab. The Cold Atom Lab is the first-ever quantum physics facility aboard the International Space Station.
Scientists took atom samples and cooled them to nearly absolute zero (minus 459 degrees Fahrenheit, or minus 273 degrees Celsius). It is the lowest temperature matter can reach. Later, they shaped them into extremely thin, hollow spheres. The cold gas begins as a small, round blob, similar to an egg yolk, shaped into a thin eggshell. Similar experiments on Earth have failed: the atoms pool downward. As a result, it generates something that looks more like a contact lens than a bubble.
The ultracold bubbles could eventually be used in new experiments with an even more exotic material: the fifth state of matter called a Bose-Einstein condensate (BEC).
Scientists created ultracold bubbles in a tightly sealed vacuum chamber. Magnetic fields were used to manipulate the gas into different shapes. The largest bubbles are about 1 millimeter in diameter and 1 micron thick. They are so thin and dilute that only thousands of atoms compose them. A cubic millimeter of air on Earth contains somewhere around a billion trillion molecules.
David Aveline, lead author of the new work and a member of the Cold Atom Lab science team at NASA’s Jet Propulsion Laboratory in Southern California, said, “These are not like your average soap bubbles. Nothing in nature gets as cold as the atomic gases produced in Cold Atom Lab. So we start with this unique gas and study how it behaves when shaped into fundamentally different geometries. And, historically, when a material is manipulated in this way, very interesting physics and new applications can emerge.”
Exposing materials to different physical conditions is essential to understanding their behavior. Gravity is the vital force that impacts the motion and behavior of fluids. Conducting these types of experiments on the space station using the Cold Atom Lab enables scientists to remove the effects of gravity. It also helps better understand other factors, such as a liquid’s surface tension or viscosity.
Nathan Lundblad, a professor of physics at Bates College in Lewiston, Maine, and the principal investigator of the new study, said, “Some theoretical work suggests that if we work with one of these bubbles that is in the BEC state, we might be able to form vortices – basically, little whirlpools – in the quantum material. That’s one example of a physical configuration that could help us understand BEC properties better and gain more insight into the nature of quantum matter.”
The next step for scientists involves transitioning the ultracold gas composing the bubbles to the BEC state. Next, they will then determine how it behaves.
- Carollo, R.A., Aveline, D.C., Rhyno, B. et al. Observation of ultracold atomic bubbles in orbital microgravity. Nature (2022). DOI: 10.1038/s41586-022-04639-8