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Above photo: Dr. Menno Veldhorst and Prof. Andrew Dzurak with some of the instruments they used to test concepts for their design while at the Centre of Excellence for Quantum Computation and Communication Technology./ Credit: UNSW

Above photo: Dr. Menno Veldhorst and Prof. Andrew Dzurak with some of the instruments they used to test concepts for their design while at the Centre of Excellence for Quantum Computation and Communication Technology./ Credit: UNSW

UNSW engineers create complete design for quantum computer chip using standard silicon technology

Engineers at the University of New South Wales (UNSW) have published a complete design for a quantum computer chip, that can be manufactured using mostly standard industry processes and components.

The new chip design, published in the journal Nature Communications, details a novel architecture that allows quantum calculations to be performed using existing semiconductor components, known as CMOS (complementary metal-oxide-semiconductor) – the basis for all modern chips. It’s the first attempt to integrate into a single chip all of the conventional silicon circuitry needed to control and read the millions of qubits needed for quantum computing.

The design was devised by Professor Andrew Dzurak, director of the Australian National Fabrication Facility at the University of New South Wales (UNSW), and Dr. Menno Veldhorst, lead author of the paper who was a research fellow at UNSW when the conceptual work was done.

A quantum computer exponentially expands the vocabulary of binary code used in modern computers’. At the subatomic level, the laws of classical physics no longer apply.  Particles can exist in more than one state at a time. Quantum computing utilises these so-called spooky quantum-mechanical phenomena, superposition and entanglement, to perform operations on data. Entanglement occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle (such as the polarisation of a photon) cannot be described independently of the others, even when the particles are separated by a large distance, while superposition states that any two (or more) quantum states can be added together and the result will be another valid quantum state.

A classical bit can be in one of two states, 0 or 1, whereas a single qubit or quantum bit can represent a 1, a 0 or any quantum superposition of those two qubit states. This would allow a universal quantum computer to be millions of times faster than any conventional computer when solving a range of important problems.

For some challenging problems they could find solutions in days, or even hours, which today’s fastest supercomputers would take millions of years to solve. But to solve these complex problems like cancer and global challenges like climate change, a useful universal quantum computer will need a large number of qubits, possibly millions, packed together and integrated like in modern microprocessor chips.

The press release from UNSW explains that there are at least five major quantum computing approaches being explored worldwide: silicon spin qubits, ion traps, superconducting loops, diamond vacancies and topological qubits (this backgrounder document provides brief introductions to the different approaches). UNSW’s design is based on silicon spin qubits. But there has been no clear pathway till now to scaling the number of quantum bits up to the millions needed, without the computer becoming huge a system requiring bulky supporting equipment and costly infrastructure.

Moreover, all known types of qubits are fragile, and even tiny errors can be quickly amplified into wrong answers.

The new design from the UNSW researchers incorporates conventional silicon transistor switches to ‘turn on’ operations between qubits in a vast two-dimensional array, using a protocol similar to that used to select bits in a conventional computer memory chip. By selecting electrodes above a qubit, a qubit’s spin can be controlled, which stores the quantum binary code of a 0 or 1. And by selecting electrodes between the qubits, two-qubit logic interactions, or calculations, can be performed between qubits.

The design also incorporates error-correcting codes which employ multiple qubits to store a single piece of data. Our chip blueprint incorporates a new type of error-correcting code designed specifically for spin qubits, and involves a sophisticated protocol of operations across the millions of qubits.

Prof. Dzurak, who is also a Program Leader at Australia’s Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), said, ““We often think of landing on the Moon as humanity’s greatest technological marvel. But creating a microprocessor chip with a billion operating devices integrated together to work like a symphony – that you can carry in your pocket! – is an astounding technical achievement, and one that’s revolutionised modern life. With quantum computing, we are on the verge of another technological leap that could be as deep and transformative. But a complete engineering design to realise this on a single chip has been elusive. I think what we have developed at UNSW now makes that possible. And most importantly, it can be made in a modern semiconductor manufacturing plant.”

Above photo: The Australian National Fabrication Facility (ANFF) at UNSW, where the qubits are manufactured./ Credit: UNSW

Veldhorst, now a team leader in quantum technology at QuTech – a collaboration between Delft University of Technology and TNO, the Netherlands Organisation for Applied Scientific Research – said the power of the new design is that, for the first time, it charts a conceivable engineering pathway toward creating millions of quantum bits, or qubits.

Other CQC2T researchers involved in the design published in the Nature Communications paper were Henry Yang and Gertjan Eenink, the latter of whom has since joined Veldhorst at QuTech.

Only two years ago, in a paper in Nature, Prof. Dzurak and Dr. Veldhorst showed, for the first time, how quantum logic calculations could be done in a real silicon device, with the creation of a two-qubit logic gate – the central building block of a quantum computer.

“Those were the first baby steps, the first demonstrations of how to turn this radical quantum computing concept into a practical device using components that underpin all modern computing. Our team now has a blueprint for scaling that up dramatically,” said Mark Hoffman, UNSW’s Dean of Engineering.

“We’ve been testing elements of this design in the lab, with very positive results. We just need to keep building on that – which is still a hell of a challenge, but the groundwork is there, and it’s very encouraging. It will still take great engineering to bring quantum computing to commercial reality, but clearly the work we see from this extraordinary team at CQC2T puts Australia in the driver’s seat,” he added.

The UNSW team has struck a A$83 million deal between UNSW, Telstra, Commonwealth Bank and the Australian and New South Wales governments to develop, a 10-qubit prototype silicon quantum integrated circuit by 2022 – the first step in building the world’s first quantum computer in silicon.

In August, the partners launched Silicon Quantum Computing Pty. Ltd., Australia’s first quantum computing company, to advance the development and commercialisation of the team’s unique technologies. The NSW Government pledged AU$8.7 million, UNSW AU$25 million, the Commonwealth Bank AU$14 million, Telstra AU$10 million and the Australian Government AU$25 million.

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