Breakthrough discovery brings quantum computing chips with billions of qubits closer

EDSR intrinsic rotation

How can multiple qubits be controlled using the new “core spin-orbit EDSR” process? Credit: Tony Milov

The detection of a previously unknown effect enables compact and very fast control of spin qubits.

Australian engineers have discovered a new way to precisely control the single electrons in quantum dots that operate logic gates. Moreover, the new mechanism is slimmer and requires fewer parts, which may prove necessary to make silicon quantum computers a reality.

A serendipitous discovery made by engineers V.I[{” attribute=””>quantum computing start-up Diraq and UNSW Sydney, is detailed on January 12 in the journal Nature Nanotechnology.

“This was a completely new effect we’d never seen before, which we didn’t quite understand at first,” said lead author Dr. Will Gilbert, a quantum processor engineer at Diraq, a UNSW spin-off company based at its Sydney campus. “But it quickly became clear that this was a powerful new way of controlling spins in a quantum dot. And that was super exciting.”

Single Qubit Flip

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

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

Deraq engineers have discovered a new way to precisely control the single electrons contained in quantum dots that operate logic gates, bringing the reality of achieving a billion-qubit quantum chip closer. Moreover, the new mechanism is slimmer and requires fewer parts, which may prove necessary to make silicon quantum computers a reality. Credit: Diraq

Use electric fields instead of magnetic fields

While experimenting with different geometries of billionths of a meter-sized devices that control quantum dots, along with different types of tiny magnets and antennas driving their operation, Dr. Tomo Tanto stumbled upon a strange effect.

“I was really trying to run a two-qubit gate accurately, with many different hardware iterations, slightly different geometries, different material stacks, and different control techniques,” recalls Dr. Tanto, a measurement engineer at Deraq. Then this strange peak appeared. It looked as if the spin rate of one of the qubits was speeding up, which I had never seen in four years of doing these experiments.”

The engineers later realized that what he had discovered was a new way to manipulate the quantum state of an individual qubit using qubits Electrician fields, instead of the magnetic fields they were using earlier. Since the discovery was made in 2020, the engineers have worked to perfect the technology — which has become another tool in their arsenal to fulfill Dirag’s ambition of building billions of qubits on a single chip.

Speed ​​up Qubit until it starts clattering

Illustration of a single qubit when it starts to accelerate in response to a microwave signal, and an electron starts to vibrate inside the quantum dot. Credit: Tony Milov

“This is a new way to manipulate qubits, and it’s much less bulky in construction — you don’t need to fabricate a small cobalt magnet or antenna next to the qubits to generate the control effect,” Gilbert said. “It removes the requirement to put additional structures around each gate. So, there is less clutter.”

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

“Normally, we design microwave antennas to deliver purely magnetic fields,” said Dr. Tanto. But this particular antenna design generated more electric field than we wanted—and that turned out to be lucky, because we discovered a new effect that we can use to manipulate qubits. This is a coincidence for you.”

Drag Research Team

Prof. Andrew Dzurak, Dr. Will Gilbert, and Dr. Tomoe Tanto of Deraq Quantum Computing Corporation. Credit: Grant Turner

The discovery brings quantum computing closer to silicon

“This is a gem of a new mechanism, which only adds to the proprietary suite of technology we’ve developed over the past 20 years of research,” said Professor Andrew Dzorak, CEO and founder of Deraq, and professor of quantum engineering at the University of New South Wales. , who led the team that built the first quantum logic gate in silicon in 2015.

“It builds on our work to make quantum computing in silicon a reality, essentially based on the same semiconductor component technology as current computer chips, rather than on 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 to commercial production and achieve our goal of manufacturing billions of qubits on a single chip.”

Peach lab

A bird’s-eye view of one of the Deraq laboratories in Sydney, Australia. Credit: Sean Dougherty

CMOS (or Complementary Metal Oxide Semiconductor, pronounced “C-Mos”) 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.

Building a quantum computer has been called the “space race of the 21st century” — a grueling and ambitious challenge with the potential to offer revolutionary tools to tackle otherwise impossible computations, such as designing complex medicines and advanced materials, or fast searching from huge unclassified databases.

“We often think of the moon landing as humanity’s greatest technological marvel,” said Dzurak. “But the reality is that today’s CMOS chips — with billions of actuators fused together to act like a symphony, that you carry in your pocket — is an amazing technical achievement, revolutionizing modern life. Quantum computing would be just as amazing.”

Reference: “On-demand electrical control of spin qubits” by Will Gilbert, Tomo Tanto, Wei Han Lim, Mengke Feng, Jonathan Y. Huang, Jesus de Cifuentes, Santiago Serrano, Philip Y. May, Ross C.C. Leon, Christopher C. . Escott, Kohei M. Itoh, Nikolay V. Abrosimov, Hans-Joachim Pohl, Michael LW Thewalt, Fay E. Hudson, Andrea Morello, Arne Laucht, Chih Hwan Yang, Andre Saraiva and Andrew S. Dzurak, Jan. 12 2023, Nature’s Nanotechnology.
DOI: 10.1038/s41565-022-01280-4

About Diraq

Diraq aims to redefine scalable quantum computing by creating billions of qubits on a single chip, compared to the hundreds of qubits possible today. Drawing on proprietary technology developed over 20 years of research and with over A$100 million in funding across nine patent pools, Diraq’s approach builds on existing silicon manufacturing processes that foundries use to produce current-generation semiconductor components, known as CMOS, for faster and cheaper configuration. . way to market. It aims to be an end-to-end quantum computing provider, creating quantum hardware and software as an integrated service that can be accessed through the cloud.

About UNSW Engineering

UNSW Engineering is a powerhouse of engineering research in Australia, made up of nine schools and 36 research centres. Ranked in the top 50 engineering schools in the world and equal fifth globally in sustainability (equally first in Australia); It also ranks first in Australia for graduates creating start-ups. The University of New South Wales itself leads the list of Australian universities with the largest number of millionaire alumni.

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