The new spin control method approximates a billion-qubit quantum chip

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.

The serendipitous discovery, made by engineers at quantum computing startup Diraq and UNSW Sydney, is detailed in the journal Nature’s Nanotechnology.

“This was a completely new effect that we hadn’t seen before, and one that we didn’t fully understand at first,” said lead author Dr. Will Gilbert, a quantum processor engineer at Diraq, a University of New South Wales subsidiary based in Sydney. Campus. “But it soon became clear that this was a powerful new way to control spin in a quantum dot. And that was very exciting.”

Logic gates are the basic building block of all computational operations; They allow “bits” — or binary numbers (0 and 1) — to work together to process information. However, a qubit (or qubit) exists in both states at once, a condition known as “superposition”. This allows for many computation strategies—some dramatically faster, others to operate simultaneously—that are beyond conventional computers. Qubits itself is made up of “Quantum dots“Small nanodevices that can trap one or a few electrons. Precise control of electrons is necessary for computation to occur.”

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, iterating across lots of different devices, slightly different geometries, different stacks of materials, and different control techniques,” recalls Dr. Tanto, a measurement engineer at Deraq. “Then there was this strange peak. It seemed that 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 a single individual qubit Using electric fields, instead of the magnetic fields they were using earlier. Since the discovery was made in 2020, 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.

“This is a new way to manipulate qubits, and it’s much less bulky in construction — you don’t need to fabricate micro-cobalt magnets or an antenna right 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 recognized methods:Electron spin resonance(ESR) using an on-chip microwave antenna; and dipole spin resonance (EDSR), which is based on an induced gradient magnetic field. The newly discovered technique is known as “EDSR in intrinsic spin orbit”.

“Normally, we design our 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. ”

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 Dirag, and professor of quantum engineering at UNSW. , 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 commercial production and achieve our goal of manufacturing billions of qubits at a time.” single slide. ”

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 for 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 quickly 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.”