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Physics Colloquium - Dr Ashton Bradley

Monday, 1 July 2019

Physics Department

Dr Ashton Bradley

Department of Physics

University of Otago

"Giant vortex clusters in a quantum fluid"

Atomic Bose-Einstein condensates (BECs) provide a uniquely controllable setting in which to study quantum fluid dynamics. In a stirred superfluid, quantized vortices typically proliferate, injecting linear and angular momentum into the fluid. In 1949, while studying the point-vortex model, Onsager predicted that confinement of quantum vortices can produce a surprising result: the possibility of vortices reaching negative temperatures. Negative temperature states contain significant energy, forming a collective storm of vortices circulating in the same direction: a giant vortex cluster. Vortex cluster states are the quantum analogue of the Great Red Spot, visible on the surface of Jupiter as a manifestation of classical fluid turbulence. I will describe our work on the theory of giant vortex clusters, and joint work with the BEC group at the University of Queensland to observe them for the first time in a quantum gas controlled by a digital micromirror device. Despite expectations that such high energy states should be unstable, we observe giant quantum vortex clusters with very long lifetimes. Our work confirms Onsager’s prediction after some 70 years, and opens the door to a new regime for quantum vortex matter at negative absolute temperatures, with implications for quantum turbulence, helium films, nonlinear optical materials, and fermi superfluids.

WHEN: Monday 1 July 2019
WHERE: Room 314, Science 3 Building
TIME: 3.00 pm–4.00 pm

All interested are welcome to attend

Light refreshments to follow in Common Room