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Details of Grant 

EPSRC Reference: EP/R005192/1
Title: Quantum vortex reconnections in trapped Bose-Einstein condensates
Principal Investigator: Barenghi, Professor CF
Other Investigators:
Parker, Dr NG
Researcher Co-Investigators:
Dr L Galantucci
Project Partners:
University of Trento
Department: Sch of Maths, Statistics and Physics
Organisation: Newcastle University
Scheme: Standard Research
Starts: 01 October 2017 Ends: 30 September 2020 Value (£): 374,496
EPSRC Research Topic Classifications:
Cold Atomic Species Quantum Fluids & Solids
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
25 Apr 2017 EPSRC Physical Sciences - April 2017 Announced
Summary on Grant Application Form
Long, almost one dimensional structures (filaments) are ubiquitous in the universe, consisting of chains of atoms (macromolecules) or regions of concentrated field lines (vortex lines in fluids, magnetic flux tubes in electrically conducting plasmas). Filaments occur at the microscopic scale of proteins and DNA, through the intermediate scales of tornadoes, dust devils and the trails behind planes and boats, up to the huge scales of the star-forming clouds in outer space. When two filaments come close to each other, they can split and recombine, having exchanged strands. Such reconnection events not only change the geometry of the filaments themselves but they also change the underlying topology (the property for which two rings which are linked to each other are different from two rings which are separated). A better understanding of reconnections is therefore crucial to many problems in the natural sciences and in engineering (for example, how the energy of a fluid is spread by reconnections).

With reconnections arising across many distinct physical contexts and over many scales, it is natural to ask whether any behaviours are universal, such that a shared framework of understanding can be sought. For example, the loss of energy during a reconnection in a fluid is directly analogous to that which occurs during a reconnection in a plasma despite different physical origins of the loss of energy (viscosity in the fluid and electrical resistivity in the plasma). Other examples debated in the scientific community are whether a measure of the coiling, twisting and linking of the filaments, termed the helicity, is conserved during reconnections, and whether complicated tangled knots of filaments may decay or disentangle in ways which depend on the topology rather than the physical nature of the system. Our understanding of reconnections is still in its infancy and would benefit from detailed quantitative measurements of reconnections, and from comparison of reconnections across different scientific disciplines.

In this context, trapped atomic Bose-Einstein condensates (BECs) provide an ideal testing ground to study reconnections. BECs are gases of atoms, cooled to within a few billionths of a degree above absolute zero. Here the blurry laws of quantum mechanics rule and transform the gas into a quantum fluid. This type of fluid is remarkable in its simplicity: while everyday fluids possess viscosity and can form tornadoes of any size or shape, quantum fluids have no viscosity and their tornadoes have a fixed size and shape. This makes them easier to conceptualise, model and understand. What is more, experimentalists are able to control and manipulate the fluid, and its vortices, to a high level of precision.

Our recent preliminary work in collaboration with an experimental group in Trento, Italy, not only demonstrated reconnections in BECs for the first time, but also revealed new and unexpected forms of reconnections. Motivated by this, we will perform detailed computer simulations of vortex reconnections in the ideal context provided by BECs, determining exactly how reconnections occur and what their consequences are. Then, by comparing to the behaviour in different settings (ordinary fluids, plasmas and macromolecules) we will probe whether universal behaviours do exist (for example, if the distance between reconnecting strands scales with time with a universal power law, or if energy losses relate to the amount of knottedness), probing the relation between energy and topology in different systems.

To disseminate our results across scientific communities, we will organise an interdisciplinary workshop on reconnections with the top experts from atomic physics, astrophysics, fluid dynamics, knot theory, with a view to building a common picture. Close collaboration with the ongoing experiment at Trento will guide our theoretical studies and provide immediate experimental tests of our findings.

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