Quantum computing at the nanoscale – News – The University of Sydney

Sometimes youd be the only person in the world with this new piece of knowledge. Its a pretty wild feeling

Professor David Reilly

Its been said that quantum computing will be like going from candlelight to electric light in the way it will transform how we live. Quite a picture, but what exactly is quantum computing?

For the answer to that question, well have to visit a scale of existence so small that the usual rules of physics are warped, stretched and broken, and there are few layperson terms to lean on. Strap yourself in.

Luckily, we have a world-leading researcher in quantum computing, Professor David Reilly, to guide us. Most modern technologies are largely based on electromagnetism and Newtonian mechanics, says Reilly in a meeting room at the Universitys Nano Hub. Quantum computing taps into an enormous new area of nano physics that we havent harnessed yet.

With his youthful looks and laid-back demeanour, Reilly isnt how you might picture a quantum physicist. He has five Fender guitars (with not much time to play them), and a weakness for single malt Scotches. That said, science has never been far below the surface. As a child, he would pull apart flashlights to see how they worked. During his PhD years, knowledge was more important than sleep; he often worked past 3am to finish experiments.

Sometimes youd be the only person in the world with this new piece of knowledge. Its a pretty wild feeling. A good place to start the quantum computing story is with the humble transistor, which is simply a switch that allows, blocks or varies the flow of electricity, or more correctly, electrons. Invented in 1947, it replaced the large, energy-hungry vacuum tubes in radios and amplifiers, also finding its way into computers.

This off/on gate effect of transistors is the origin of the zeroes and ones idea in traditional (aka classical) computers. Ever-shrinking transistors are also how computers have gone from room-filing monsters to tiny devices in our pockets currently, just one square millimetre of computer chip can hold 100 million transistors.

Incredible, yes, but also unsustainable. With transistors now operating at the size of atoms, they literally cant get much smaller, and theyre now at a scale where the different, nanoscale laws of physics are warping and compromising their usefulness. At that scale, an electron stops behaving like a ball being stopped by the transistor gate, Reilly says. Its more like a wave. It can actually tunnel through or teleport to the other side, so the on/off effect is lost.

Quantum computing seeks to solve this problem, but it also promises a great leap forward. Its based on the idea that transistors can be replaced by actual atomic particles where the zeros and ones arent predicated on the flow or non-flow of electrons, but on the property or energy state of the atomic particle itself.

These particles can come from various sources (and are usually engineered in nanoscale devices) but theyre called collectively, qubits. Now things get trickier. Yes, tricker. Where a transistor can be either one or zero, its a weird fact of quantum physics, that a qubit can be one or zero at the same time, like a spinning coin that holds the possibility of both heads and tails.

For a single qubit, this doubles the one-andzero mechanism. And for every qubit added, the one/zero combinations increase exponentially.

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Quantum computing at the nanoscale - News - The University of Sydney