Sydney researchers drive advances in quantum computing

Sydney researchers have successfully reduced errors in semiconductor “spin qubits” – a type of building block for quantum computers.

This has been achieved using the theoretical work of quantum physicists at the University of Sydney Nano Institute and School of Physics.

The experimental result by University of New South Wales engineers demonstrated error rates as low as 0.043 percent, lower than any other spin qubit.

The joint research paper by the Sydney and UNSW teams was published this week in Nature Electronics and is the journal’s cover story for April.

Professor Stephen Bartlett, a corresponding author of the paper, said reducing errors in quantum computers is needed before they can be scaled up into useful machines.

“Once they operate at scale, quantum computers could deliver on their great promise to solve problems beyond the capacity of even the largest supercomputers. This could help humanity solve problems in chemistry, drug design and industry,” said Bartlett.

There are many types of quantum bits, or qubits, ranging from those using trapped ions, superconducting loops or photons.

A “spin qubit” is a quantum bit that encodes information based on the quantised magnetic direction of a quantum object, such as an electron.

Australia, and Sydney in particular, is emerging as a global leader in quantum technology. The recent announcement to fund the establishment of a Sydney Quantum Academy, underlines the huge opportunity in Australia to build a quantum economy based on the world’s largest concentration of quantum research groups here in Sydney.

While much of the recent focus in quantum computing has been on advances in hardware, none of these advances have been possible without the development of quantum information theory.

The University of Sydney quantum theory group, led by Bartlett and Professor Steven Flammia, is one of the world powerhouses of quantum information theory, allowing for engineering and experimental teams across the globe make the painstaking physical advances needed to ensure quantum computing becomes a reality.

The work of the Sydney quantum theory group was essential for the world-record result published in Nature Electronics.

Bartlett said because the error rate was so small, the UNSW team needed some pretty sophisticated methods to even be able to detect the errors.

“With such low error rates, we needed data runs that went for days and days just to collect the statistics to show the occasional error.”

Once the errors were identified they needed to be characterised, eliminated and recharacterised.

“Flammia’s group are world leaders in the theory of error characterisation, which was used to achieve this result,” he said.

The Flammia group recently demonstrated for the first time an improvement in quantum computers using codes designed to detect and discard errors in the logic gates, or switches, using the IBM Q quantum computer.

Fully functioning quantum computers will need millions, if not billions, of qubits to operate. Designing low-error qubits now is a vital step to scaling up to such devices.

The joint University of Sydney-UNSW result comes soon after a paper by the same quantum theory team with experimentalists at the Niels Bohr Institute in Copenhagen.

That result, published in Nature Communications, allows for the distant exchange of information between electrons via a mediator, improving the prospects for a scaled-up architecture in spin-qubit quantum computers.

The result was significant because it allows for the distance between quantum dots to be large enough for integration into more traditional microelectronics.

The achievement was a joint endeavour by physicists in Copenhagen, Sydney and Purdue in the US.