Electrons and qubits: Explaining quantum computing

Research impact and institutes 23rd February 2023

You can probably age a person fairly accurately depending on how they react to the word “quantum”.

Something to do with Ant-Man? That Bond film that wasn’t as good as Casino Royale? Did Sam ever make the final leap home? Even – if you’re of a certain age – the name of that 70s band who had a hit with a bizarre song about the Lone Ranger.

Well, chances are that in the next few years, “quantum” will come to mean something quite different, in a way that touches us all, as developments in what’s known as quantum computing are poised to revolutionise the way in which computers work.

To get an idea of what we mean by quantum computing, and the implications for the future, we met with Richard Curry, Professor of Advanced Electronic Materials in the Department of Electrical and Electronic Engineering. Richard is also Vice-Dean for Research and Innovation, and an expert in the field.

We began by asking: what do we actually mean by “quantum”?

Richard Curry: Quantum is the study and use of very, very small objects, which most people will be familiar with as atoms and electrons – which form part of atoms. And when we have objects that are so small on that scale, the way they behave is described by something called quantum theory. And this has interesting and sometimes difficult to conceptualise results, depending on what it is we’re looking to study or do with them.

Dave Espley: So to a layperson, then, does quantum in that sense mean “very small” or is that too simplistic?

Richard: It does mean very small. And the reason why it’s very small is that there is a fundamental constant called Planck’s constant, which effectively describes the size of objects at which we start to see quantum behaviour emerging. And it just so happens that in our universe, this constant means that things have to be on the nanometre size – tens of nanometres, typically – before we start to see and observe quantum behaviour. At larger scales that quantum behaviour, such as the wave behaviour of particles, is kind of hidden away. So, yes, it does mean very small, but there’s always some situations where bigger objects may display quantum behaviour under very special circumstances.

Dave: A lot of the current excitement is around quantum computing. What is quantum computing?

Richard: There’s been a lot of research and interest in quantum recently, and something called Quantum 2.0 has emerged. And what Quantum 2.0 is moving towards is starting to use some of these strange properties which we find in quantum mechanics. A computer – which everyone has on a desk, or in a phone – still relies on some quantum properties, such as electrons being able to tunnel through what are called barriers. Quantum 2.0 is one step beyond that; it’s taking dual properties of materials – of electrons, for example – and using that nature itself to manipulate information in a way which we can’t using standard computing.

Dave: Could you tell us a bit more about “qubits”?

Richard: Qubits are at the heart of quantum computing. The analogy with a classical computer is that in those we operate using bits, which are either zero or one. In the quantum world, something can be one or zero or a combination of those, at the same time. What that means is that it can take all the values between zero and one at the same time, and we can operate on all of those values at the same time and then get the result out at the end. So what it enables us to do is address problems which we couldn’t normally do using standard computing because we’d have to run the program for so long to cover all of the different variables and opportunities that the system could exhibit, that we’d never get to a solution.

Dave: Does that mean computer technicians need to rethink the way they build computers?

Richard: Yeah, absolutely. A quantum computer isn’t built like your standard computer. And one of the key challenges in quantum mechanics is that if we interfere with the quantum system, we effectively lose all the information. “Interfere” means look at it, it means measure it whilst it’s doing these operations – and measuring it doesn’t just mean us physically measuring something, it means interacting with its environment. It’s actually one of the strengths in cryptography, which is an example that many people have used early on: that if someone does interfere with the system, you know about it. And so you can tell if anyone has eavesdropped on your communication.

Dave: What kind of real world examples might we be looking at in terms of what quantum computing can give us?

Richard: There’s many areas of application of quantum computing. Some of them are the “travelling salesman”-type problems – optimisation problems. Some of them are in security, making sure that your bank data and your communications are secure, and others are in the design of very complex systems. And some of those complex systems are going to be drugs. And if we’re looking for personalised medicine, then in the future it would be great if someone has a diagnosis of some sort of illness, and we can take information about that person and that illness, combine it together and design a bespoke drug which targets exactly the need to help realise a cure or treatment for that individual. We can’t do that at the moment.

Thanks to Richard for speaking to us. If you’d like to hear more from him on this fascinating subject, you can listen to the full conversation below.