Australian-made quantum computer reaches 99% accuracy milestone

A recent research paper recently published in the Nature journal has demonstrated that “near error-free quantum computing is possible”, with the silicone-based platform achieving 1-qubit operation fidelities up to 99.95 per cent and 2-qubit fidelities of 99.37 per cent.

The accuracy of the findings was verified using gate set tomography, originally developed at Sandia National Laboratories in the United States.

In addition to these breakthrough findings, research leader Professor Andrea Morello confirmed that the team's quantum solution was able to contain quantum information in silicone for some 35 seconds.

“In the quantum world, 35 seconds is an eternity,” Professor Morello said.

“To give a comparison, in the famous Google and IBM superconducting quantum computers the lifetime is about a hundred microseconds – nearly a million times shorter.”

According to a release, the academic leaps didn’t come without a trade-off.

To achieve the 35-second information preservation, the qubits were isolated to a point where they were unable to communicate as required to undertake complex computations.

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However, the team managed to circumvent the challenge by utilising an electron with two nuclei of phosphorous atoms.

“If you have two nuclei that are connected to the same electron, you can make them do a quantum operation,” Dr Mateusz Mądzik, one of the lead authors noted.

“While you don't operate the electron, those nuclei safely store their quantum information. But now you have the option of making them talk to each other via the electron, to realise universal quantum operations that can be adapted to any computational problem.”

Dr Serwan Asaad, another lead author of the experiment, explained how the team hoped to transform the research into computational capabilities.

“This really is an unlocking technology,” Asaad explained.

“The nuclear spins are the core quantum processor. If you entangle them with the electron, then the electron can then be moved to another place and entangled with other qubit nuclei further afield, opening the way to making large arrays of qubits capable of robust and useful computations.”

David Jamieson, lead researcher at the University of Melbourne, explained how the team achieved their experimental breakthrough.

“The phosphorous atoms were introduced in the silicon chip using ion implantation, the same method used in all existing silicon computer chips. This ensures that our quantum breakthrough is compatible with the broader semiconductor industry.”

The confirmation of the new research breakthrough comes as a University of Melbourne-led team pioneered a new quantum computing manufacturing method.

The technique of building parts “atom by atom” is said to “create large scale patterns of counted atoms that are controlled so their quantum states can be manipulated, coupled and read-out”.

The findings were published in an Advanced Materials paper and were developed by Professor David Jamieson and his team from UNSW Sydney, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Leibniz Institute of Surface Engineering (IOM) and RMIT.

According to Professor Jamieson, the team’s goal is to develop a large quantum device with this scalable method.

“We believe we ultimately could make large-scale machines based on single atom quantum bits by using our method and taking advantage of the manufacturing techniques that the semiconductor industry has perfected,” Professor Jamieson said.

To develop the chip, the researchers have to be precise to within the nanometre.

“The technique takes advantage of the precision of the atomic force microscope, which has a sharp cantilever that 'touches' the surface of a chip with a positioning accuracy of just half a nanometre, about the same as the spacing between atoms in a silicon crystal,” a spokesperson from the University of Melbourne explained.

During the process, the team would “drop” an atom through a hole in the cantilever onto its correct position on the chip. The sound of the atom colliding with the silicone enabled the researchers to know when the atom was in place, enabling the researchers to construct items with single atoms more precisely than previous trials.

“One atom colliding with a piece of silicon makes a very faint click, but we have invented very sensitive electronics used to detect the click, it's much amplified and gives a loud signal, a loud and reliable signal,” Professor Jamieson explained.

“That allows us to be very confident of our method. We can say, ‘Oh, there was a click. An atom just arrived. Now we can move the cantilever to the next spot and wait for the next atom’.”

UNSW's Professor Morello, co-author of the paper, explained that resulting prototype was a qubit “chip”, which was later used in experiments to understand the scalability of the process.

“This will allow us to engineer the quantum logic operations between large arrays of individual atoms, retaining highly accurate operations across the whole processor,” Professor Morello said.

“Instead of implanting many atoms in random locations and selecting the ones that work best, they will now be placed in an orderly array, similar to the transistors in conventional semiconductors computer chips.”

The University of Melbourne’s Dr Alexander (Melvin) Jakob, first author of the paper, explained that the equipment used was designed as part of an internationally collaborative process.

“We used advanced technology developed for sensitive X-ray detectors and a special atomic force microscope originally developed for the Rosetta space mission along with a comprehensive computer model for the trajectory of ions implanted into silicon, developed in collaboration with our colleagues in Germany,” Dr Jakob said.

“With our Centre partners, we have already produced groundbreaking results on single atom qubits made with this technique, but the new discovery will accelerate our work on large-scale devices.”

It is hoped that quantum computers will be able to process new ways of breaking cryptography, optimising finance and even potentially vaccine development.

The University of Melbourne project was supported by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, the US Army Research Office as well as a grant from the University of Melbourne Research and Infrastructure Fund. The project utilised the Australian National Fabrication Facility at the Melbourne Centre for Nanofabrication to conduct the experimentation.

[Related: Thales enters quantum technology partnership]