Abstract
Reconnections and interactions of filamentary coherent structures play a fundamental role in the dynamics of fluids, redistributing energy and helicity among the length scales and inducing fine-scale turbulent mixing. Unlike ordinary fluids, where vorticity is a continuous field, in quantum fluids vorticity is concentrated into discrete (quantized) vortex lines turning vortex reconnections into isolated events, making it conceptually easier to study. Here, we report experimental and numerical observations of three-dimensional quantum vortex interactions in a cigar-shaped atomic Bose-Einstein condensate. In addition to standard reconnections, already numerically and experimentally observed in homogeneous systems away from boundaries, we show that double reconnections, rebounds, and ejections can also occur as a consequence of the nonhomogeneous, confined nature of the system.
1 More- Received 27 January 2017
DOI:https://doi.org/10.1103/PhysRevX.7.021031
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Long, almost one-dimensional structures known as filaments are ubiquitous. Chains of atoms such as DNA molecules, ropelike magnetic fields in electrically conducting plasmas, strings in liquid crystals, and narrow beams of light all exhibit filamentary behavior. As these filaments evolve, they interact with one another and may reconnect, exchanging neighboring strands and modifying the structure of the underlying field. These interactions play a key role in the dynamics of many types of fluids. Cigar-shaped Bose-Einstein condensates (BECs)—a type of quantum fluid cooled to nearly absolute zero—offer a useful platform for studying filament interactions. Because the circulation of the fluid is quantized, reconnections are isolated dramatic events that are easier to study than in other systems.
We have developed an innovative experimental imaging technique that allows us to track quantum vortices with unprecedented resolution, providing direct evidence of vortex reconnections in quantum fluids. Combining experiments and numerical modeling, we unambiguously identify novel vortex interactions—such as rebounds, double reconnections, and ejections—arising from the confined and inhomogeneous nature of trapped atomic BECs. These newly identified interactions go beyond the simple standard reconnections already observed in superfluid helium, and they are likely to be important in the dynamics of turbulent BECs, where more than two vortices are present.
Our imaging technique sets up BECs as an ideal experimental platform for testing the recent suggestion that some properties of filament reconnections may be universal in nature. The processes that we identify could be a key starting point for better understanding the behavior of superfluids near their boundaries.