A fermion walked into a bar…

Sean Bourelle
Friday 26 June 2015

Hello, everyone! Week 5 for me, and I am currently representing a Quantum Mechanical system using balls and springs – only in physics!

I began my project just a few days after my last exam. First I worked to reproduce the initial results obtained by Max, one of the PhD students in physics, thus familiarizing myself with the project so far, and reminding myself how to use Mathematica (the programming language that I would be working in). This involved modelling the “jump” of an optical harmonic trapping potential that contains a lattice of non-interacting fermions.

Instead of falling to the base of the potential gradient—like you would expect from balls rolling into a valley—some of the fermions become “Bragg Localised”. This means that the system acts as though there is an invisible barrier that kicks our figurative balls back up the side of the hill if they start to move too quickly— thus preventing them from rolling to the valley floor. Fortunately, my model also demonstrated this, so I then moved on to simplifying the problem using those balls and springs.

I modelled the centre of mass of the system as a ball on a spring, and a compression wave within the fermion gas as a secondary ball and spring. This reproduced the same centre of mass motion as that observed within the quenched fermionic cloud.

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Introducing the Bragg localisation effect to this simple scenario has proved a little more challenging; however, I have it working now, and am working to match parameters in my simple model to those in the trap-jumped fermionic cloud system. My main problem is, of course, all the error messages while coding!

With half the people I know graduating this week, I am looking forward to graduation weekend to catch up with friends!

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