An illustration of a vortex tangle. (Courtesy of Wei Guo/FAMU-FSU College of Engineering)

Researchers advance understanding of vortex diffusion in superfluidics

An illustration of a vortex tangle. (Courtesy of Wei Guo/FAMU-FSU College of Engineering)

An international team of scientists with researchers from Florida State University has developed a model that predicts the distribution of vortices in so-called superfluidics, work that provides new insight into the physics that controls turbulence in quantum fluid systems such as superfluid neutron stars.

In a paper published in Physical Assessment Letters, the researchers developed a model describing the spread and speed of tornado-like vortex tubes in superfluidics. Vortex tubes are an important ingredient of turbulence, which is widely studied in classical physics. The movement of vortex tubes is relevant in a wide variety of scenarios, such as the formation of hurricanes, the transmission of viruses through the air and the chemical mixing in star formation. But it is poorly understood in quantum fluids.

From left to right Wei Guo, an associate professor of mechanical engineering at the FAMU-FSU College of Engineering, and Yuan Tang, a postdoctoral researcher at the National High Magnetic Field Laboratory, in front of an experimental setup.  (Courtesy of Wei Guo)
From left to right Wei Guo, an associate professor of mechanical engineering at the FAMU-FSU College of Engineering, and Yuan Tang, a postdoctoral researcher at the National High Magnetic Field Laboratory, in front of an experimental setup. (Courtesy of Wei Guo)

This work builds on a previous study reporting experimental results obtained in superfluid helium-4 within a narrow temperature range. Superfluidics are fluids that can flow without resistance, and therefore without loss of kinetic energy. When stirred, they form vortices that rotate indefinitely.

“By validating this model and showing that it describes the motion of vortices over a wide temperature range, we confirm a universal rule for this phenomenon,” said Wei Guo, an associate professor of mechanical engineering at the FAMU-FSU College of Engineering. † “This discovery may aid in the development of advanced theoretical models of quantum fluid turbulence.”

In the previous study, Guo and his team traced the vortex tubes that appeared in superfluid helium-4, a quantum liquid that exists at extremely low temperatures. In that study, the team used tiny particles trapped in the vertebrae to track their movement. They found that the vortices spread much faster than you’d expect from the seemingly random movement of the tubes. This rapid diffusion is known as superdiffusion.

In the latest work, the researchers built a numerical model and used findings from their previous study to validate the model’s accuracy by reproducing experimental results. That allowed them to predict how vortex tubes might form and propagate within superfluids at a wider temperature range. The simulation also provided unequivocal evidence to support the physical mechanism the authors proposed to explain the observed vortex superdiffusion.

Researchers want to understand turbulence in quantum fluids for the benefits of basic research and for possible use in practical applications, such as nanowire fabrication. Vortex tubes attract particles that group together in incredibly thin lines. By controlling that process, so-called nanowires can be made, which have a thickness that is measured in nanometers.

“Particle dispersion in turbulent flow is a very active topic in the classical turbulence field, but it has received less attention in the quantum fluid community,” said Yuan Tang, a co-lead author and a postdoctoral researcher at FSU’s National Laboratory for High Magnetics field. “Our work may spur more future research on particle dispersion in quantum fluids.”

Paper co-authors include Satoshi Yui and Makoto Tsubota of Osaka Metropolitan University, Japan, and Hiromichi Kobayashi of Keio University, Japan. This article was selected by Physical Review Letters as an editor’s suggestion, a designation for articles that are particularly important, interesting, and well-written.

This research was supported by the National Science Foundation and the United States Department of Energy. Additional resources were provided by Florida State University’s National High Magnetic Field Laboratory, which is supported by the National Science Foundation and the State of Florida. This work was also supported by the Japan Society for the Promotion of Science.

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