Physicists watch as ultracold atoms form a crystal of quantum tornadoes

(Phys.org) MIT physicists have directly observed the interplay of interactions and quantum mechanics in a particular state of matter: a spinning fluid of ultracold atoms. Researchers have predicted that, in a rotating fluid, interactions will dominate and drive the particles to exhibit exotic, never-before-seen behaviors.
In a study published in Nature, the MIT team has rapidly rotated a quantum fluid of ultracold atoms. They watched as the initially round cloud of atoms first deformed into a thin, needle-like structure. Then, at the point when classical effects should be suppressed, leaving solely interactions and quantum laws to dominate the atoms’ behavior, the needle spontaneously broke into a crystalline pattern, resembling a string of miniature, quantum tornadoes.
“This crystallization is driven purely by interactions, and tells us we’re going from the classical world to the quantum world,” says Richard Fletcher, assistant professor of physics at MIT.
The results are the first direct, in-situ documentation of the evolution of a rapidly-rotating quantum gas. Martin Zwierlein, the Thomas A. Frank Professor of Physics at MIT, says the evolution of the spinning atoms is broadly similar to how Earth’s rotation spins up large-scale weather patterns.
In their new study, the physicists used lasers to trap a cloud of about 1 million sodium atoms, and cooled the atoms to temperatures of about 100 nanokelvins. They then used a system of electromagnets to generate a trap to confine the atoms, and collectively spun the atoms around, like marbles in a bowl, at about 100 rotations per second.
The team imaged the cloud with a camera, capturing a perspective similar to a child’s when facing towards the center on a playground carousel. After about 100 milliseconds, the researchers observed that the atoms spun into a long, needle-like structure, which reached a critical, quantum thinness.
“In a classical fluid, like cigarette smoke, it would just keep getting thinner,” Zwierlein says. “But in the quantum world, a fluid reaches a limit to how thin it can get.”
“This evolution connects to the idea of how a butterfly in China can create a storm here, due to instabilities that set off turbulence,” Zwierlein explains. “Here, we have quantum weather: The fluid, just from its quantum instabilities, fragments into this crystalline structure of smaller clouds and vortices. And it’s a breakthrough to be able to see these quantum effects directly.”