9 Mar 2017

Proof - the physics of creating a gas droplet

From Our Changing World, 9:06 pm on 9 March 2017

The University of Otago's Blair Blakie and Danny Baillie are theoretical physicists. A lot of their work involves thinking, but they say they are more like architects than philosophers. They design theories that experimental physicists can test - or they can come up with a theory to explain a new finding.

Theoretical gas droplet

Researchers in Dunedin came up with a theory about making a self-contained 'droplet' of gas, that could exist at very low temperatures without a container. Photo: Danny Baillie / University of Otago

Recently they ‘designed’ a theory about an ultra cold gas ‘droplet’, which a German team later confirmed in an experiment.

Danny says the the droplet is able to hold itself together in the absence of a container, much like a liquid droplet does, despite the gas droplet being about a billion times lower density than typical liquids.

Danny explains the video:

'This movie shows the preparation of a cold quantum gas into a self-bound droplet state. Initially the Bose-Einstein condensate (extremely cold quantum gas) is held together by a container called a “trap”, which is indicated for reference by the cage-like set of lines in the movies. As the trap is removed the local interactions between the atoms (quantified by the parameter a_s) is changed causing the gas to collapse into a droplet. The droplet is able to hold itself together with the absence of a container, much like a liquid droplet, despite this droplet being about a billion times lower density than typical liquids!

Along the way as the droplet forms some atoms are shed and escape, and the droplet is excited into a complex breathing like oscillation. The various coloured surfaces indicate the density of the gas. The densest regions are coloured blue, next densest green, then yellow and the lowest density parts are colour red.

The movie is prepared from the results of a computational simulation of the quantum mechanical equations describing this system and was carried out using NeSI, New Zealand's high performance computing service.

This movie is an example of the simulations carried out in the paper Self-bound dipolar droplet: A localized matter wave in free space. Experiments have now reported observing these droplets.'

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