UNSW Engineers discover a New Spin Technique, another breakthrough for the Quantum Industry

Harnessing Quantum Spin

Engineers from UNSW Sydney have developed a novel method of precisely regulating individual electrons tucked away in quantum dots that operate logic gates. The new technique is also less complicated and needs fewer components, which may be crucial for realizing large-scale silicon quantum computers.

“This was a completely new effect we’d never seen before, which we didn’t quite understand at first. But it quickly became clear that this was a powerful new way of controlling spins in a quantum dot. And that was super exciting.”

Dr Will Gilbert, a quantum processor engineer at Diraq, UNSW spin-off company based at its Kensington campus & LEad AUthor

The fundamental building component of all computation is a logic gate. They make it possible for “bits,” or binary digits (0s and 1s), to cooperate and process data. A quantum bit, also known as a qubit, can exist in both of these states simultaneously, a situation known as a “superposition.”

Dr. Tuomo Tanttu from UNSW Engineering discovered a peculiar phenomenon when testing with various geometrical configurations of devices just billionths of a meter in size that govern quantum dots and numerous sorts of tiny magnets and antennas that drive their activities.

“I was trying to really accurately operate a two-qubit gate, iterating through a lot of different devices, slightly different geometries, different materials stacks and different control techniques. “Then this strange peak popped up. It looked like the rate of rotation for one of the qubits was speeding up, which I’d never seen in four years of running these experiments.”

Dr. Tuomo Tanttu, measurement engineer at Diraq.

The engineers later realized that what he had uncovered was a novel method for controlling the quantum state of a single qubit by using electric fields instead of the magnetic fields they had previously used. The engineers have been honing the technology since the discovery was discovered in 2020. It has now become another weapon in their toolbox for realizing Diraq’s goal of assembling billions of qubits on a single chip.

“This is a new way to manipulate qubits, and it’s less bulky to build – you don’t need to fabricate cobalt micro-magnets or an antenna right next to the qubits to generate the control effect. It removes the requirement of placing extra structures around each gate. So, there’s less clutter.”

Dr Will Gilbert, a quantum processor engineer at Diraq, UNSW spin-off company based at its Kensington campus & LEad AUthor

For quantum information processing in silicon, controlling a single electron without affecting surrounding neighbors is crucial. There are two recognized methods: electron spin resonance (ESR) employing an on-chip microwave antenna, and electric dipole spin resonance (EDSR), which relies on an induced gradient magnetic field. Intrinsic spin-orbit EDSR is the name of the recently discovered method.

The Future of Silicon-based Quantum Computers

Modern computers are made using a technique called complementary metal-oxide semiconductor, or CMOS (pronounced “see-moss”). It is used to create a variety of integrated circuit parts, such as image sensors, data converters, and digital logic circuits like microprocessors and microcontrollers.

“We often think of landing on the Moon as humanity’s greatest technological marvel. But the truth is, today’s CMOS chips – with billions of operating devices integrated together to work like a symphony, and that you carry in your pocket – that’s an astounding technical achievement and one that’s revolutionised modern life. Quantum computing will be equally astonishing.”

Professor Dzurak.

“This is a gem of a new mechanism, which just adds to the trove of proprietary technology we’ve developed over the past 20 years of research. “It builds on our work to make quantum computing in silicon a reality, based on essentially the same semiconductor component technology as existing computer chips, rather than relying on exotic materials. Since it’s based on the same CMOS technology as today’s computer industry, our approach will make it easier and faster to scale up for commercial production and achieve our goal of fabricating billions of qubits on a single chip.”

Professor Andrew Dzurak, Scientia Professor in Quantum Engineering at UNSW and CEO and founder of Diraq

Read more about it here.