Elucidating the law of vortex diffusion in quantum turbulence

A research group of Professor Makoto Tsubota and Specially Appointed Assistant Professor Satoshi Yui, both from the Graduate School of Science and the Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, in cooperation with their colleagues from Florida State University and Keio University, revealed that there are laws of vortex diffusion in superfluid helium-4 (He II) at extremely low temperatures, near absolute zero (−273°C). In this study, by conducting a systematic numerical study and comparing the results with experimental observations, the research group found that quantum vortices cause "superdiffusion" over short periods of time and "normal diffusion" over longer periods of time, similar to the movement of pollen in still water.

Snapshot of simulated quantum turbulence: Cores of quantum vortices (green) with tracked particles (purple)

A research group of Professor Makoto Tsubota and Specially Appointed Assistant Professor Satoshi Yui, both from the Graduate School of Science and the Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, in cooperation with their colleagues from Florida State University and Keio University, conducted a systematic numerical study of vortex diffusion in quantum turbulence in superfluid helium-4 (He II) at extremely low temperatures, near absolute zero (−273°C), and compared the results with experimental observations.

The research team used a computer simulation to study quantum turbulence in superfluid helium-4. They inserted particles that followed tangles, which are hairball-like quantum, and analyzed the particles’ trajectory.

The systematic numerical study revealed that vortices first underwent “superdiffusion,” spreading quickly over a short time period, and then transitioned to “normal diffusion” over a longer time period. This transition is thought to be due to the reconnection of vortices when they encounter each other.

The simulation results were consistent with experimental observations, creating a possible further means of understanding complex quantum turbulence.

Furthermore, simulations over a wide range of temperatures, from absolute zero to roughly 2 K (equal to −271°C), showed insignificant changes in the “superdiffusion” index. This indicates a robust law of “superdiffusion” that is not heavily dependent on parameters such as temperature.

“In this study, we investigated the diffusion of particles in a quantum fluid at cryogenic temperatures and found that the transition from ‘superdiffusion’ to ‘normal diffusion’ depends on the time,” concluded Professor Tsubota. “This law may provide a new way to understand complex quantum turbulence.”

 

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Published: 06 Jul 2022

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Title: Universal anomalous diffusion of quantized vortices in ultraquantum turbulence
DOI: 10.1103/PhysRevLett.129.025301
Author: Satoshi Yui, Yuan Tang, Wei Guo, Hiromichi Kobayashi, and Makoto Tsubota
URL: https://doi.org/10.1103/PhysRevLett.129.025301
Publication date: July 5, 2022

Funding information:

Y.T. and W.G. are supported by the National Science Foundation under Grant DMR-2100790 and the US Department of Energy under Grant DE-SC0020113. They also acknowledge the support and resources provided by the National High Magnetic Field Laboratory at Florida State University, which is supported by the National Science Foundation Cooperative Agreement No. DMR-1644779 and the state of Florida. S.Y. is supported by the Grant-in-Aid for JSPS Fellow program under Grant No. JP19J00967. M.T. acknowledges the support by the JSPS KAKENHI program under Grant No. JP20H01855. H.K. acknowledges the support by the JSPS KAKENHI program under Grant No. JP22H01403.