Mystery Object in Ultracold Superfluids Identified in New Simulation

Computational algorithms show whirlpools, not disks, form and dissipate on fluid’s surface.

default-alt-text — Image courtesy of Argonne National Laboratory

The Science

Tiny whirlpools meander through ultracold superfluids and decay into simple vortex lines. Because these whirlpools or vortex rings appear identical to disk-shaped defects when viewed in two dimensions, the true nature of the defects was only revealed by full three-dimensional analysis.

The Impact

Realistically modeling imperfections that appear under experimental conditions provides new insights into the behavior of ultracold superfluids, or liquids cooled until they flow without friction. The presence of topological alterations and disruptions within the superfluid remains a central mystery of physics, with broad applications in cosmology and fluid dynamics.

Summary

Experiments with ultracold superfluids, specifically Fermi gases, allow scientists to investigate quantum mechanical principles central to our understanding of the physical world. Researchers developed computational algorithms that consider the complex physics of Fermi gases. The new codes can account for instabilities, including dissipation, a phenomenon through which vortices displace energy. By introducing small, experimentally unavoidable symmetry breaking, the new simulations show that the whirlpools or vortex rings rapidly decay into more stable vortex lines. The disc-like solitons that had been postulated were not present in the superfluid. Stable vortex rings were not present either. Indeed, the only stable defects were vortex lines. Recent experiments confirm that the simulations properly identified the defects. The findings also show that the numerical simulations can realistically simulate quantum mechanical phenomena in superfluids.

Contact

Andreas Glatz
Argonne National Laboratory, Materials Science Division
Argonne, Illinois
[email protected]

Kathy Levin
University of Chicago, Department of Physics & James Frank Institute
Chicago, Illinois
[email protected]

Funding

The National Science Foundation Materials Research Science and Engineering Center Grant No. 0820054 supported the research. Work at Argonne National Laboratory was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by the U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research (for large-scale graphics processing unit (GPU) simulations) and Basic Energy Sciences programs, and by the Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (for modeling and analysis). The numerical work was performed on Northern Illinois University’s Gaea GPU cluster.

Publications

P. Scherpelz, K. Padavić, A. Rançon, A. Glatz, I.S. Aranson, K. Levin. “Phase imprinting in equilibrating Fermi gases: The transience of vortex rings and other defects.” Physical Review Letters 113, 125301 (2014). [DOI: 10.1103/PhysRevLett.113.125301]