UNSW unveils complete design of a silicon quantum computer chip

A team of engineers from the University of New South Wales (UNSW) has unveiled the design of a working chip that can integrate quantum interactions.

According to UNSW, the design, which can be manufactured using mostly standard industry processes and components, comprises a "novel architecture" that allows quantum calculations to be performed using existing semiconductor components, known as CMOS -- complementary metal-oxide-semiconductor. CMOS is the basis for all modern chips.

"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," Andrew Dzurak, director of the Australian National Fabrication Facility at UNSW, said.

"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."

The chip design, published in the journal Nature Communications, was devised by Dzurak alongside Dr Menno Veldhorst, who is the lead author of the paper and was a research fellow at UNSW when the conceptual work was performed.

"Remarkable as they are, today's computer chips cannot harness the quantum effects needed to solve the really important problems that quantum computers will," Veldhorst added.

Instead, a large number of working quantum bits (qubits) will need to work in tandem to achieve the processing power quantum computers are slated to deliver.

"Our design incorporates conventional silicon transistor switches to 'turn on' operations between qubits in a vast two-dimensional array, using a grid-based 'word' and 'bit' select protocol similar to that used to select bits in a conventional computer memory chip," he added.

"By selecting electrodes above a qubit, we can control a qubit's spin, 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."

As a useful universal quantum computer will require a large number of qubits, the engineers at the university need to use error-correcting codes that 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. 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," Dzurak explained.

Dzurak, who is also a program leader at Australia's Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), expects there will still be modifications required before the chip moves towards manufacture, but said all of the key components that are needed for quantum computing are in the one chip.

"That's what will be needed if we are to make quantum computers a workhorse for calculations that are well beyond today's computers," Dzurak added. "It shows how to integrate the millions of qubits needed to realise the true promise of quantum computing."

Dzurak was instrumental in building a quantum logic gate in silicon, which made calculations between two qubits of information possible.

At the time, the discovery was called a landmark result not only for Australia, but also for the world, as until then it had not been possible to make two quantum bits "talk" to each other and create a logic gate using silicon.

"This result means that all of the fundamental building blocks that are required to make a full-scale silicon processor chip are now in place," Dzurak said previously. "We're ready to move from this scientific research phase, into the engineering stage and the manufacturing stage."

Building on this breakthrough, another team of researchers out of the university, led by professor Michelle Simmons, unlocked the key to enabling quantum computer coding in silicon, announcing in late 2015 that the team had the capability to write and manipulate a quantum version of computer code using two qubits in a silicon microchip.

Quantum computing is expected to revolutionise the world, with Australia well placed to be the first across the quantum finish line.

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