New spin control method brings quantum chips closer to billions of qubits

New spin control method brings quantum chips closer to billions of qubits

How multiple qubits can be controlled using the new “intrinsic spin-orbit EDSR” process. Credit: Tony Melov

Australian engineers have discovered a new way to precisely control individual electrons housed in quantum dots that run logic gates. In addition, the new mechanism is less bulky and requires fewer parts, which could prove essential to making large-scale silicon quantum computers a reality.


The serendipitous discovery, made by engineers at quantum computing start-up Diraq and UNSW Sydney, is detailed in the journal. Nanotechnology of nature.

“This was a completely new effect that we hadn’t seen before, that we didn’t really understand at first,” said lead author Dr. Will Gilbert, a quantum processor engineer at Diraq, a company spin-off of UNSW based in Sydney. campus. “But it quickly became clear that this was a powerful new way to control spins in a quantum dot. And that was super exciting.”

Logic gates are the basic building block of all calculations; they allow “bits” – or binary digits (0s and 1s) – to work together to process information. However, a quantum bit (or qubit) exists in both states simultaneously, a condition known as “superposition”. This allows for a multitude of computational strategies—some exponentially faster, others operating simultaneously—that go beyond classical computers. Qubits themselves are made up of “quantum dots,” tiny nanodevices that can trap one or a few electrons. Precise control of the electrons is necessary for the calculation to take place.

Diraq engineers have discovered a new way to precisely control individual electrons housed in quantum dots that run logic gates, bringing the realization of billion-qubit quantum chips closer to reality. In addition, the new mechanism is less bulky and requires fewer parts, which could prove essential to making large-scale silicon quantum computers a reality. Credit: Diraq

Using electric rather than magnetic fields

While experimenting with different geometric combinations of devices only billionths of a meter in size that control quantum dots, along with different types of magnets and tiny antennas that drive their operations, Dr. Tuomo Tanttu came across a strange effect.

“I tried to really operate a two-qubit gate by iterating a lot of different devices, slightly different geometries, different material stacks, and different control techniques,” recalls Dr. Tanttu, a measurement engineer at Diraq. “Then this strange spike appeared. It looked like the spin speed of one of the qubits was increasing, which I’ve never seen in four years of running these experiments.”

What he had discovered, the engineers later realized, was a new way to manipulate the quantum state of a single qubit by using electric fields rather than the magnetic fields they had previously used. Since the discovery was made in 2020, engineers have perfected the technique – which has become another tool in their arsenal to fulfill Diraq’s ambition to build billions of qubits on a single chip.

New spin control method brings quantum chips closer to billions of qubits

Artist’s concept of a single qubit held in a quantum dot flipping in response to a microwave signal. Credit: Tony Melov

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

Controlling single electrons without disturbing others nearby is essential for quantum information processing in silicon. There are two established methods: “electron spin resonance” (ESR) using an on-chip microwave antenna; and electric spin dipole resonance (EDSR), which is based on an induced gradient magnetic field. The newly discovered technique is known as “intrinsic spin-orbit EDSR”.

“We normally design our microwave antennas to deliver purely magnetic fields,” Dr Tanttu said. “But this particular antenna design generated more of an electric field than we wanted – and it turned out to be lucky, because we discovered a new effect that we can use to manipulate qubits. This is serendipity for you.”

New spin control method brings quantum chips closer to billions of qubits

Bird’s eye view of one of Diraq’s laboratories in Sydney, Australia. Credit: Shaun Dougherty

Discovery brings quantum computing closer to silicon

“This is a gem of a new mechanism that only adds to the trove of proprietary technology we have developed over the past 20 years of research,” said Professor Andrew Dzurak, CEO and founder of Diraq and professor of quantum engineering at UNSW. , who led the team that built the first silicon quantum logic gate in 2015.

“It builds on our work to make silicon quantum computing a reality, based on essentially the same semiconductor component technology as existing computer chips, rather than exotic materials,” he added. “Because it is based on the same CMOS technology as the computer industry today, 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.”

CMOS (or complementary metal-oxide-semiconductor, pronounced “see-moss”) is the manufacturing process at the heart of modern computers. It is used to make all kinds of integrated circuit components, including microprocessors, microcontrollers, memory chips and other digital logic circuits, as well as analog circuits such as image sensors and data converters.

New spin control method brings quantum chips closer to billions of qubits

Illustration of a single qubit as the ir begins to accelerate in response to a microwave signal and the electron begins to rattle around in the quantum dot. Credit: Tony Melov

Building a quantum computer has been called “the space race of the 21st century” – a difficult and ambitious challenge with the potential to provide revolutionary tools for tackling otherwise impossible calculations, such as the design of complex drugs and advanced materials or fast search. of massive, unsorted databases.

“We often think of the moon landing as humanity’s greatest technological marvel,” Dzurak said. “But the truth is that today’s CMOS chips—with billions of operating devices integrated together to work like a symphony and carried in your pocket—is an astonishing technical achievement, and one that has revolutionized modern life. Quantum computing will be just as mind-blowing. .”

More information:
Will Gilbert, On-demand electrical control of spin qubits, Nanotechnology of nature (2023). DOI: 10.1038/s41565-022-01280-4. www.nature.com/articles/s41565-022-01280-4

Citation: New spin-control method brings billion-qubit quantum chips closer (2023, January 12) Retrieved January 12, 2023, from https://phys.org/news/2023-01-method-billion-qubit-quantum -chips-closer.html

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