Superfluids — also called quantum fluids — appear in a wide range of systems and applications. For example, cosmological superfluids meld with each other during neutron star mergers, and scientists use superfluid helium to cool magnetic resonance imaging (MRI) machines.

The fluids have unique and useful properties governed by quantum mechanics — a framework usually used to describe the realm of the very small. For superfluids, however, these quantum mechanical properties dominate on a larger, macroscopic scale. For example, superfluids lack viscosity, a sort of internal friction that allows the fluid to resist and cause motion.

This lack of viscosity grants the liquids unusual abilities, like traveling freely through pipes with no loss of energy or remaining still inside a spinning container. But when it comes to rotational motion, scientists struggle to understand how rotating superfluids transfer angular momentum — a quality that speaks to how fast the liquids will spin.

In a recent study, scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory collaborated with scientists from the National High Magnetic Field Laboratory (MagLab) in Tallahassee, Florida, and Osaka City University in Japan to perform advanced computer simulations of merging rotating superfluids, revealing a peculiar corkscrew-shaped mechanism that drives the fluids into rotation without the need for viscosity.

When a rotating raindrop falls into a pond, viscosity enables the drop to drive the surrounding water into rotation, generating vortices or eddy currents in the process. This viscous drag reduces the difference in motion between the two bodies. A superfluid, however, allows this difference.

The atoms stay roughly in the same place when superfluids transfer angular momentum, unlike with eddy currents in classical fluids,” said Dafei Jin, a scientist at Argonne’s Center for Nanoscale Materials (CNM), a DOE Office of Science User Facility. ​Rather than through the convection of particles, it’s more efficient for superfluid atoms to transfer angular momentum through quantum mechanical interactions.”

These quantum mechanical interactions give rise to a mesmerizing effect, exhibited in the team’s simulations performed using the Carbon computer cluster at CNM. The scientists simulated the merging of rotating and stationary drops of a superfluid state of matter called a Bose-Einstein Condensate (BEC).

Read more at Argonne National Laboratory.

Image: Merging dynamics of two BECs, one rotating and one stationary. Density evolution of each drop is shown in the top row, and angular momentum transfer is shown in the bottom row. Angular momentum is transferred due to the spontaneous emergence of a corkscrew structure at the interface. (Image by the Center for Nanoscale Materials.)