A quantum leap

By Travis Taylor

Since their arrival on the scene in the 1940’s computers have changed dramatically.

The earliest computers used gears and vacuum tubes to function; today’s computers run on miniscule logic gates, transistors and silicon chips that perform calculations with mind-bending speed and accuracy.

And they’ve changed the way we live almost every facet of our lives – there’s little left out there without a computer chip in it.

Yet despite this, and the massive impact computers have had, there’s a new technology lurking that could have just as significant an impact as the digital revolution.

Though it’s a technology still in its infancy, the idea of encoding and processing information in quantum systems – and using quantum computers – is being hailed by many as a technology that could spark a new technological age.

Dr Lanyon and the prototype quantum computer.

Dr Benjamin Lanyon is a quantum physicist in the School of Maths and Physics at the University of Queensland (UQ), and is at the forefront of this exiting new area of research.

“I work in the field, essentially, of quantum information,” he said.

“The aim of which is to investigate the capabilities of encoding and processing information in physical systems that are so small, they must be described using the bizarre laws of quantum physics”

“At UQ we’ve got a node of the ARC Centre of Excellence for Quantum Computer Technology.”

“The Centre’s devoted to trying to build a new type of information processor that’s radically different from the way people have been building and going about processing information in the past.”

Dr Lanyon said the research was based on the principles of quantum mechanics, an area of physics that was essentially about the very small – the world of the subatomic.

He said particles of a subatomic size, such as electrons and photons, behaved very strangely.

“The idea is that you can exploit their strange behaviour to do very powerful information processing tasks and all kinds of strange ‘Star Trek’ like things,” Dr Lanyon said.

Traditional digital computers are built on the power of processing bits (0’s and 1’s) encoded into physical systems that follow the laws of everyday `classical’ physics.

In a traditional computer, a set of two bits gives four unique configurations (00, 01, 10, and 11); but the two bits can only be in one configuration at a time.

On the other hand, quantum computers use quantum bits – qubits – encoded in physical systems that follow the laws of quantum mechanics.

In a quantum computer, a set of two qubits can, in some sense, be in all four unique configurations at the same time - a state known to physicists as a `quantum superposition’.

“A qubit is like a coin that can be heads (on), tails (off) or simultaneously heads AND tails (on and off) or any possible combination in-between,” Dr Lanyon said.

“This is impossible with normal bits, but a qubit can be in two possible states, two qubits can be in four, three qubits in eight, and so on – so quantum memory sizes grow exponentially with the number of qubits.”

Dr Lanyon’s research focuses on using light from lasers as a base for these qubits, and hence, quantum computing.

“If you turn light down to a very low intensity and have a sensitive enough detector, you’ll find that it has a particulate nature to it – it comes in discrete bits called photons,” he said.

“We’re trying to use these quantum particles, the quantum particles of light, as the carriers of quantum information.”

“And so we’re in the lab and we’ve got lots of shiny lasers and we’re bouncing them around with mirrors, trying to get them to talk to each other and we’re actually trying to build the very first small prototype quantum computers.”

To do this, Dr Lanyon said he and his colleagues had to construct a number of quantum logic gates to process the photons (qubits).

“Your everyday computer, mobile phone or mp3 player has logic gates in it and you can do any kind of operation you want by just re-arranging your logic gates; they’re the building blocks of your computer,” Dr Lanyon said.

“In a normal computer nowadays you might have hundreds of millions of logic gates: we have a couple – a handful – of quantum logic gates and that’s where we’re at.”

“Just trying to understand them, how to characterize them, how to make them work better, we’re really at that very basic stage, and we’d need a large number of these before we’d be able to do things your normal computer wouldn’t be able to do.

While Dr Lanyon said they weren’t yet at that stage, they’d still managed to build a working prototype quantum computer.

“Although we’ve built a very small quantum computer we’re not ready to just go and make it bigger and bigger,” he said.

“It’s a real experimental challenge to build even a single one of these quantum logic gates because you require such a high level of control over your system.”

“You don’t want to lose all your particles and photons and things; it’s very easy to lose them and they’re very fragile.”

“I think there are still some physical obstacles that we need to overcome in the path to scalability, but there’s none that we know of that are just no goers, that we’ll never be able to overcome,” Dr Lanyon said.

“We’re almost at a stage where we need massive investment from engineering companies and whoever in order to get the technology that we need.”

Dr Lanyon said that along with the fragility of the logic gates holding back the development of a quantum iMac, there was also the issue of size.

“These things are massive in comparison to the single transistor chips that are inside your computer, which are on the microscopic scale,” he said.

“We’re building single logic gates that are a foot across.”

But Dr Lanyon said going much smaller is certainly feasible, and that this is an active research area.

“At the moment we’re trying to understand them, so we need to get in there with screw drivers and things like this, but eventually, once you really understand them, you can micro fabricate them down into very small devices,” he said.

“If you think about the first computers, which were these huge things that took up whole rooms, it’s a nice comparison to where we’re at.”

So they’ve managed to build a basic quantum computer, but what can they do with it?

“You run algorithms in computers and they solve problems that are interesting,” Dr Lanyon said.

“There are some algorithms that have been written for quantum computers that solve interesting problems, one of them is code cracking and another’s simulating physical systems – which are typically so complicated that normal computers can’t get their heads around.”

Dr Lanyon and his colleagues were among the first in the world to successfully execute one of these algorithms on a quantum computer.

“We demonstrated the simplest problem of this code breaking instance and it’s actually finding the prime factors of numbers; so 15 for example, the prime factors are 3 and 5,” Dr Lanyon said.

“So we used our very small scale quantum computer to run the algorithm that can calculate the prime factors of numbers and we worked out, surprise surprise, that the prime factors of 15 are three and five.”

“This isn’t something that’s hard to do at that level, but if you make the number that you’re trying to work out the factors of larger and larger, it becomes harder and harder to do it.”

“And in fact the difficulty in doing that, working out the prime factors of large numbers, is the basis for an encryption technique used around the world today as a standard for banks and the internet.”

Dr Lanyon said using a quantum computer to break this method of encryption could ultimately protect our personal information and money.

“Our goal is not to break these codes in practice, but to show that they can be broken, and motivate a move to a more secure system," Dr Lanyon said.

A major part of the significance of the work done by the team at UQ is that the algorithm that was used, and the process of using it, scales efficiently.

“So for larger numbers we wouldn’t need a quantum computer the size of the universe to solve these things, it’s something that could in principle be done efficiently.”

In another experiment, for which Dr Lanyon is currently writing a research article, the team has been able to use their prototype quantum computer, and another algorithm, to simulate and calculate the energy of a molecule.

“This new paper about simulating quantum systems, that is an early step towards using this new kind of computer as a new tool to do new research, and to test our models and understanding of the physical world,” Dr Lanyon said.

“At the moment there’s a real problem in physics where we’re trying to understand systems that are so complicated our computer systems just can’t handle them, so we can’t even test our models.

“I think that if you look back over all of the scientific developments over the last hundred, 200 years, even further back, the big revolutions have come about when we start to develop a new level of control over the world,” he said.

“Almost as if we had a new tool to hit it with in a new way; a lot of the radical new developments were generated by those results, essentially banging things in a new way and seeing how they react.”

“And this a hell of a new way to bang things.”

While Dr Lanyon acknowledges the quantum computer built at UQ is a long way off a full-scale device, he’s convinced quantum computing will be hugely important in the future.

“I think it’s fair to say that back when the transistor was invented, many decades ago, it seems unlikely that people had much of an idea what it was going to be used for,” Dr Lanyon said.

“Yet I think they knew that it had the potential to be a very powerful device in some way.

“Physicists and computer scientists have some ideas about quantum computing that could revolutionise what we could do in terms of new physics and new technology, but I think it’s fair to say that while we haven’t got a clue as to the full extent of what these things can do, we’re pretty confident that it’s going to be fairly significant.”

“People are talking about the second technological revolution, where we move to this completely new way of going about things.”