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Confirming an incredible quantum phenomenon

In fundamental physics, theory and experiment go hand-in-hand. Without theoretical modelling, it’s hard to come up with new ideas and move things forward. Experimental validation of theoretical predictions brings it all together. Nowadays, combining the power of supercomputer calculations with the delicate experimental setups that physicists are capable of can produce incredible results.

Professor Anatoli Kheifets of The Australian National University has worked with collaborators from Australia, the US and South Korea to understand a fundamental paradox at the heart of quantum mechanics. When a single electron reaches a seemingly impenetrable barrier, it can sometimes travel through it instead of reflecting back off it. This is because of the dual wave-matter nature of these tiny particles. In the right circumstances, they appear to break the rules we think we know about the material world.

This behaviour, known as quantum tunnelling, was first described in the 1920s and has led to technologies such as the scanning tunnelling microscope and the tunnelling transistor that may become a building block of electronic circuits in the future.

In quantum tunnelling devices, electrons travel through quantum gates to conduct electricity and pass information along. If we want to build these future devices, we will need to know how rapidly electrons travel through barriers and whether a tunnelling delay could slow down the performance of those future electronics. Professor Kheifets and his colleagues have now found the answer, both theoretically and experimentally.

A stylised sequence of images showing an electron passing through an electric field and its angular deviation.

A simplified illustration of the experimental process used in this research.

So how long does quantum tunnelling take? Quantum tunnelling is instantaneous. A single electron does not take any time to travel through the barrier. Like a travelling Schrödinger’s cat, it appears to be on both sides of the barrier at the same time.

Simplified theoretical models already showed this to be true four years ago, but this work brings much more detailed models to bear on the extremely complex, real-world experimental setup that the Australian Attosecond Science Facility used to conduct their actual measurements. Running thousands of simulations of electron behaviour, from all angles and directions and at the infinitesimal speeds of quantum particles, required NCI’s supercomputer as a crucial research tool.

“Super things go together: to understand something super-small or super-fast, you need a supercomputer. Because of the complexity of the super-strong laser field our electrons travel through, we need to use NCI’s supercomputing resources to measure quantum tunnelling properly,” says Professor Kheifets.

The power of a supercomputer comes from the phenomenal number of simultaneous calculations it can perform. For understanding the smallest and fastest phenomena of particle physics, as with the large and slow phenomena of galaxy formation, researchers need as much computational power as possible. Working with experimentalists, theoreticians on one of the country’s fastest supercomputers are discovering amazing things about the fundamentals of our world.

Professor Kheifets’ latest paper is published in Nature.

You can read about the original theoretical work from 2015 in this research highlight.

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