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Investigating the properties of quantum particles

Lumpy yellow and green-blue bubbles fill a 3D black grid.

Gluon and photon field fluctuations in the lattice designed by Dr James Zanotti, Mr Joshua Charvetto and Professor Derek Leinweber at the University of Adelaide.

Scientists from the University of Adelaide have been modelling the behaviour of quantum particles using Raijin’s advanced computing capabilities.

ARC Future Fellow Dr James Zanotti says, “Our group has been a heavy user of the NCI facilities, and without them our group in Adelaide would have really struggled to exist. The fact that we have access to NCI means that our measurements are able to have an impact internationally.”

He has been trying to understand protons and their quantum properties for over 15 years using the theory of Quantum Chromodynamics (QCD). One of the problems he is trying to understand is the theoretical basis for why neutrons are heavier than protons, even though they share almost all of the same properties.

To look into this question, Dr Zanotti and his team use a computer lattice that is designed to have exactly the quantum properties they are interested in, including contributions from not only QCD, but also QED (or Quantum Electrodynamics). Their current lattice is a cube shaped grid, 32 units high, long and wide, and covers a period of around 20 yoctoseconds in 64 time steps. One yoctosecond is a trillionth of a trillionth of a second, a 1 preceded by 23 zeros after the decimal point.

To understand more about the proton, they need to mathematically add various quantum background variables and the proton itself into the lattice. After all of this, they end up with a system of around 200 million distinct numbers that represent the entire lattice and everything going on inside it. Finally, they need to solve around 2 million simultaneous equations in order to calculate the behaviour of the proton over the 20 yoctoseconds of the lattice simulation.

“Because this is a quantum field you can’t just take a single snapshot of it, you need to look at the order of a thousand snapshots. So we need to generate the 200 million numbers a couple of thousand times,” explains Dr Zanotti.

That much data to compute at once makes these calculations impossible to do without sophisticated technology.

“QCD is a very complicated theory, you’re not able to solve it analytically on a piece of paper, and you can only get close to achieving this feat by performing large-scale calculations on a supercomputer,” says Dr Zanotti.

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