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UNSW scientists take key step towards world’s first Quantum computer

Lead researcher Professor Michelle Simmons in her UNSW laboratory. Photo: UNSW

A team of quantum computer physicists at UNSW Sydney have engineered a quantum processor at the atomic scale to simulate the behaviour of a small organic molecule, solving a challenge set some 60 years ago by theoretical physicist Richard Feynman.

The achievement, which occurred two years ahead of schedule, represents a major milestone in the race to build the world’s first quantum computer, and demonstrates the team’s ability to control the quantum states of electrons and atoms in silicon at an exquisite level not achieved before. Quantum science is one of the main areas of focus of DST Group’s STaR Shot program and the Next Generation Technologies Fund (NGTF).

The researchers from UNSW spin-off Silicon Quantum Computing (SQC) have mimic-ed the structure and energy states of the organic compound polyacetylene – a repeating chain of carbon and hydrogen atoms distinguished by alternating single and double bonds of carbon.

Lead researcher and former Australian of the Year, Scientia Professor Michelle Simmons, said, “We should have some kind of commercial outcome from our technology five years from now.”

She said the team at SQC built a quantum integrated circuit comprising of a chain of 10 quantum dots to simulate the precise location of atoms in the polyacetylene chain. The research relied on measuring the electric current through the replica of the polyacetylene molecule as each new electron passed from the source outlet of the device to the drain – the other end of the circuit.

To be doubly sure, they simulated two different strands of the polymer chains. Not only did the measurements match the theoretical predictions, they matched perfectly.

 “What it’s showing is that you can literally mimic what actually happens in the real molecule,” said Prof. Simmons. “And that’s why it’s exciting because the signatures of the two chains are very different.

“Most of the other quantum computing architectures out there haven’t got the ability to engineer atoms with sub-nanometer precision or allow the atoms to sit that close. And so that means that now we can start to understand more and more complicated molecules based on putting the atoms in place as if they’re mimicking the real physical system.”

A carbon chain of 10 atoms was chosen because that sits within the size limit of what a classical computer is able to compute, with up to 1024 separate interactions of electrons in that system. Increasing it to a 20-dot chain would see the number of possible interactions rise exponentially, making it difficult for a classical computer to solve.

“We’re near the limit of what classical computers can do, so it’s like stepping off the edge into the unknown,” said Prof. Simmons.

“And this is the thing that’s exciting, we can now make bigger devices that are beyond what a classical computer can model. So we can look at molecules that haven’t been simulated before. We’re going to be able to understand the world in a different way, addressing fundamental questions that we’ve never been able to solve before.”

Prof. Simmons said that the development of quantum computers is on a comparable trajectory to how classical computers evolved – from a transistor in 1947 to an integrated circuit in 1958, and then small computing chips that went into commercial products like calculators approximately five years after that.

“And so we’re now replicating that roadmap for quantum computers,” Prof. Simmons says.

“We started with a single atom transistor in 2012. And this latest result, realised in 2021 is the equivalent of the atom-scale quantum integrated circuit, two years ahead of time. If we map it to the evolution of classical computing, we’re predicting we should have some kind of commercial outcome from our technology five years from now.”

One of the advantages that the UNSW/SQC team’s research brings is that the technology is scalable because it manages to use fewer components in the circuit to control the qubits – the basic bits of quantum information.

Looking ahead, Prof. Simmons and her colleagues will explore larger compounds that may have been predicted theoretically, but have never been simulated and fully understood before, such as high temperature superconductors.

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