In the late ’90s, a senior researcher at IBM published a list of the technical hurdles facing anyone who wanted to build a quantum computer. One of the biggest would be for those wanting to make their qubits from single atoms positioned in a crystal. 'Conceivable' sure, but frankly 'pie-in-the-sky’.
“It said – you know it’s a nice idea but there are many reasons why this is not going to work. It said there’s no way to do that,” explains Professor Michelle Simmons. “The consensus view in the scientific community was that the chances of getting through all of those hurdles was pretty near impossible.”
Thanks to the work of researchers at the Centre for Quantum Computation and Communication Technology (CQC2T) in Sydney, that view is beginning to change. Simmons is proving her doubters wrong, and not for first time.
Whether she’ll succeed is barely in question. She’s not just sure, she says: “I’m convinced”.
Sold on silicon
There are potentially a number of ways to build a quantum computer. The CQC2T, housed in an unremarkable brick building on UNSW’s Kensington campus, is focusing on one method and one material: Silicon. It is making qubits, the elementary unit of a quantum computer, by encasing a single atom of phosphorus within a silicon crystal and harnessing its quantum properties.
It is a method first theorised by Bruce Kane in 1998, while at UNSW on a three-year fellowship.
“We created our centre on the basis – can we actually build that dream?” Simmons explains.
It was a calculated risk, but a risk nonetheless. Silicon is relatively cheap and has been used in the manufacturing processes of chips and computer components for many years.
“For me it was a no brainer pitch to be honest,” Simmons says. “You had this theoretical paper about an ambitious goal, there’s no doubt it was ambitious, no doubt it was high risk, but the thing that underpinned it was: If you look at the silicon industry, every year it makes devices and they get smaller and smaller and you can plot in time how small they’re going to be.
“All we were doing was saying instead of doing the iterative research and make chips smaller every year, we’re just going to jump to the point at the end where you’re making it out of a single atom.”
Simmons came to Australia in 1999, soon after Divencenzo’s paper, now considered the de facto checklist for every quantum computer builder, was published. She arrived on a fellowship to found the centre which has recently attracted the backing of the Commonwealth Bank, Telstra and the Federal Government.
Move by move
From the beginning, Simmons and the centre’s researchers mapped out each milestone towards their ultimate aim. One by one they’ve hit them (and patented the technology too).
Simmons puts this down to a strategy of having “multiple pathways in case we’ve hit a block” and a constantly “aligning to the endpoint”.
“To be successful you have to be totally focused,” Simmons says. “And you have to be systematic. And ruthless. Ruthless systematics. If you have someone on the team that’s not systematic, you can’t deviate. You have to keep everyone absolutely on the pathway.”
It’s a mindset Simmons has maintained since a young age. A defining moment in her life, she says, happened when she was eight years old, living in London with her family.
Every weekend her father and brother would play chess. Simmons watched their every move.
“One day after a fairly intense game, I asked if I could play too. The response from my father was somewhat dismissive and terse. A girl playing chess?”
He nevertheless indulged her, only half paying attention while chatting with her mother.
"After a few moves he saw that I took a piece. And I remember seeing his eyes flicker. About 20 minutes later suddenly he was fully focused on the board with me. And 25 minutes later I checkmated him. He was horrified!"
By 12 she was London girl chess champion, the first in a lifetime of accolades. At school she was the only girl in her physics class.
“Having achieved at something that was very difficult I decided to try and pick the hardest thing that I could find,” she says. “Something that I knew that I would wake up to every day, be excited about, go and do and find challenging, and get that euphoric feeling of something difficult that I could master at the end.”
In 2006, she was elected to the Australian Academy of Science, one of the youngest people to do so. In 2010 Simmons was credited in The Guinness Book of World Records as one of the creators of the world’s smallest transistors (made from seven phosphorus atoms in a silicon crystal) and in 2014 became a member of the American Academy.
“I always wanted to choose a problem that was relevant,” she says about why she decided to work in quantum computing, “and if we could do it, would lead to something useful.
“It’s fundamental. And it’s applied. And it’s hard. It’s hard with the end goal that’s worth doing.”
Whether a functional silicon-based quantum computer can actually be made remains to be seen. But with Simmons at the helm, it’s difficult to doubt.
“There are lots of different approaches,” Simmons says. “Every one has promise and every one has problems. As a scientist you’re never sure which one is going to work.
“I always say, at the end, you have one life, so you bet your life on the thing that you think is going to work. So I look at all the other approaches and I’m immensely impressed. Some people have got higher qubit numbers but they have less coherence, other people have engineered fantastic systems.
“We’ve made a bet on a material system. In 20 years’ time we may be wrong. But every time I see all this other stuff I think – thank God I’m doing what I’m doing. I’m convinced that I’m in the right one.”