Integrated quantum chip operations are now possible

Two fundamental quantum techniques have been combined by Australian researchers in an integrated silicon chip, confirming the promise of using silicon for quantum computing.

Quantum computers that are capable of solving complex problems, like drug design or machine learning, will require millions of quantum bits — or qubits — connected in an integrated way and designed to correct errors that inevitably occur in fragile quantum systems. Now, a UNSW-led research team has experimentally realised a crucial combination of these capabilities on a silicon chip.

The team is led by Professor Andrew Dzurak, a program leader at the Centre of Excellence for Quantum Computation and Communication Technology (CQC2T) and Director of the NSW node of the Australian National Fabrication Facility. He and his colleagues have demonstrated an integrated silicon qubit platform that combines both single-spin addressability — the ability to ‘write’ information on a single spin qubit without disturbing its neighbours — and a qubit ‘read-out’ process that will be vital for quantum error correction.

Last year, Prof Dzurak and colleagues published a design for a novel chip architecture that could allow quantum calculations to be performed using silicon CMOS (complementary metal-oxide-semiconductor) components — the basis of all modern computer chips. In their new study, published in the journal Nature Communications, the team combine two fundamental quantum techniques, confirming the promise of their approach.

Prof Dzurak’s team had previously shown that an integrated silicon qubit platform can operate with single-spin addressability — the ability to rotate a single spin without disturbing its neighbours. They have now combined this with a special type of quantum readout process known as Pauli spin blockade, a key requirement for quantum error correcting codes that will be necessary to ensure accuracy in large spin-based quantum computers. This new combination of qubit readout and control techniques is a central feature of their quantum chip design.

“We’ve demonstrated the ability to do Pauli spin readout in our silicon qubit device but, for the first time, we’ve also combined it with spin resonance to control the spin,” said Prof Dzurak.

“This is an important milestone for us on the path to performing quantum error correction with spin qubits, which is going to be essential for any universal quantum computer.”

The lead author on the study is Michael Fogarty, who performed the experiments as part of his PhD research. According to Fogarty, “Quantum error correction is a key requirement in creating large-scale useful quantum computing because all qubits are fragile, and you need to correct for errors as they crop up… [This] creates significant overhead in the number of physical qubits you need in order to make the system work.”

“By using silicon CMOS technology we have the ideal platform to scale to the millions of qubits we will need, and our recent results provide us with the tools to achieve spin qubit error correction in the near future,” Prof Dzurak added.

“It’s another confirmation that we’re on the right track. And it also shows that the architecture we’ve developed at UNSW has, so far, shown no roadblocks to the development of a working quantum computer chip — and, what’s more, one that can be manufactured using well-established industry processes and components.”

Working in silicon is important not just because the element is cheap and abundant, but because it has been at the heart of the global computer industry for almost 60 years. The properties of silicon are well understood and chips containing billions of conventional transistors are routinely manufactured in big production facilities.

Three years ago, Prof Dzurak’s team realised quantum logic calculations in a real silicon device with the creation of a two-qubit logic gate — the central building block of a quantum computer. Prof Mark Hoffman, UNSW’s Dean of Engineering, said, “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.

“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.”

In 2017, a consortium of Australian governments, industry and universities established Australia’s first quantum computing company to commercialise CQC2T’s intellectual property. Operating out of new laboratories at UNSW, Silicon Quantum Computing (SQC) has the target of producing a 10-qubit demonstration device in silicon by 2022, as the forerunner to creating a silicon-based quantum computer.

In May 2018, Australian Prime Minister Malcolm Turnbull and French President Emmanuel Macron announced the signing of a memorandum of understanding (MoU) addressing a new collaboration between SQC and the French research and development organisation Commissariat à l’energie atomique et aux energies alternatives (CEA), bringing together French and Australian efforts to develop a quantum computer.

The MoU outlined plans to form a joint venture in silicon-CMOS quantum computing technology to accelerate and focus technology development, as well as to capture commercialisation opportunities. The proposed JV would bring together Prof Dzurak’s team with a team led by Dr Maud Vinet from CEA, who are experts in advanced CMOS manufacturing technology, and who have also recently demonstrated a silicon qubit made using their industrial-scale prototyping facility in Grenoble.

Pictured: Illustrations of the complete quantum computer chip. Credit: Tony Melov/UNSW.