UNSW and Diraq quest for scalable hole-spin qubits

UNSW Sydney in association with start up Diraq have reached a milestone in the hunt for the perfect quantum computing storage qubit to allow faster and more efficient quantum computing applications.

The team demonstrated hole-spin qubits – positively charged particles in semiconductors – using industry standard silicon manufacturing processes.

Hole-spins qubits have the potential to revolutionise quantum computer data storage by offering rapid operation speeds and seamless integration with existing silicon technology.

The work, published in the journal Nature Communications, opens the door for quantum computers to be manufactured in existing silicon chip factories, with the potential to significantly speed up their development.

Dr Scott Liles, a postdoctoral fellow from UNSW Physics and lead author on the paper, said: “This is an important step towards a new generation of high-speed silicon quantum bits, and it’s notable that the team included researchers at all levels from undergraduate students to experienced research scientists.”

The basic building block of a quantum computer is a qubit, or a ‘quantum bit’, with a quantum chip a physical platform that houses qubits and other quantum components.

Two of the key factors that will make the best qubit are how reliably the qubits can be operated, and how easily a single qubit prototype can be scaled up to the millions of qubits needed to build a functional quantum computer.

“One potential solution is the development of hole qubits. Holes – essentially positively charged electrons in semiconductors – have been predicted to have promising properties for qubits in a quantum computer, including a rapid control speed and all electrical operation.

“In particular, silicon based qubits are attracting interest, partly because they can be integrated into the manufacturing processes that have been optimised by the multi-trillion dollar semiconductor industry.

“This means that designing qubits that are compatible with this existing manufacturing technology could allow large scale quantum computers to be produced in the same factories that make ordinary silicon chips.”

While holes are used in almost all conventional silicon chips, the techniques to fabricate hole-based qubits in silicon have not been as well developed as their electron-based counterparts.

Addressing the challenge of making the hole qubit device has been a research focus for Professor Alex Hamilton and Dr Liles working in collaboration with Diraq founder Professor Andrew Dzurak – from their first demonstrations of planar silicon hole devices using CMOS (Complementary Metal-Oxide-Semiconductor) technology, to optimising and improving the model and developing a device that uses both holes and electrons.

In their latest paper, the multidisciplinary team presents the first demonstration of a hole-based qubit on a planar MOS (metal-oxide-semiconductor) silicon structure.

Prof. Dzurak said: “This collaboration supports Diraq’s goal of creating the world’s first commercial quantum computer using silicon-chip based technology, a platform that is cost efficient, energy efficient, and due to its compact size has a small infrastructure footprint.

“Production of these semiconductor chips in commercial foundries, such as IMEC is where the economies of scale really make sense – as you can make many millions of transistors on a square centimetre of silicon, ensuring the power of quantum will be accessible, sustainable and a viable option for commercial applications.”

The team are currently working on a collaboration with commercial partner Diraq and industrial partner IMEC to look at producing these qubits using standard industry processes.

Picture: UNSW Sydney/Daniel Halverson, Prof. Alexander Hamilton & Dr. Scott Liles