Quantum computing at the nanoscale

It’s 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, we’ll 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 University’s Nano Hub. “Quantum computing taps into an enormous new area of nano physics that we haven’t harnessed yet.”

With his youthful looks and laid-back demeanour, Reilly isn’t 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 you’d be the only person in the world with this new piece of knowledge. It’s 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 can’t get much smaller, and they’re 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. “It’s 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. It’s based on the idea that transistors can be replaced by actual atomic particles where the zeros and ones aren’t 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 they’re called collectively, qubits. Now things get trickier. Yes, tricker. Where a transistor can be either one or zero, it’s 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.

It is envisaged that quantum computers could have billions of qubits, representing phenomenal computing power. That’s very broadly the theory, but what currently keeps Reilly up at night is how to build the machinery that will allow the theory to impact the real world.

This machine would need a mechanism for manipulating the state of the qubits and a way of inputting and outputting information. As an added challenge, to make it all controllable, the machine would have to operate at minus 273°C, just a shade above absolute zero. “How to do all that is technically and fundamentally challenging. There are big scientific questions, big engineering questions, but that’s what we do here,” Reilly says, unflustered.

The quality of the work happening at the Hub was powerfully endorsed in 2017, when the Microsoft Corporation proposed a research partnership with the University, one of only four such arrangements Microsoft has in the world. “This is not a research grant," Reilly says. “Microsoft have been working in quantum computing since 2005 and they’re in it for the long haul. Now we’re working together, elbow to elbow in the labs, on something where every part is a work in progress.

It’s a partnership advancing a frontier.” Reilly’s role sees him straddling the corporate and the academic, where deep knowledge is important but always with the goal of creating something real. Remembering how even great work can vanish into academic papers, Reilly says, “The thought of not knowing whether this technology can come alive, I find to be scary. Connecting the discovery bit to the industry engineering machine means you actually see the whole system come together. That’s exciting.”

So, where might quantum computing be put to work? The first thing to know is that our classical computers will not disappear from homes or offices. Quantum computers work on a scale well beyond emails, video games and spreadsheets. They will be about hugely accelerating global research and production.

“If you look at the top 10, classicaltype super computers on the planet right now, you’ll find some are doing defence applications, like simulating weapons,” Reilly says. “But a big chunk of them, are renting time out to pharmaceutical companies to understand the basic chemistry of different types of drugs which is really complex stuff.”

These are the areas – industrial chemistry, pharmaceuticals, climate, city planning – where quantum computing could bring unimagined speed and accuracy, and the possibility of much more.

“Go back to the invention of things like the transistor and you’ll see that humankind’s ability to imagine what a new technology might do in the longer term is pretty poor. “Likewise, this new physics promises new technology,” says Reilly. “And chances are, it will be revolutionary.”

Written by George Dodd. Photography by Louise M Cooper.