Spin qubit control method promises scalable silicon quantum computing
Engineers at the quantum computing startup Diraq say they have discovered a new way of precisely controlling single electrons in quantum dots that run logic gates – the basic building block of all computation. The new technique is less bulky and needs fewer parts – essential to making large-scale silicon quantum computers a reality.
This discovery of a previously unknown effect, say the researchers, makes compact, ultra-fast control of spin qubits for quantum computers possible.
“This was a completely new effect we’d never seen before,” says lead author Dr. Will Gilbert, an engineer at Diraq, a UNSW spin-off based at the university’s Sydney campus, Australia. “But it quickly became clear that this was a powerful new way of controlling spins in a quantum dot. And that was super exciting.”
Logic gates 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, known as a ‘superposition,’ which allows a multitude of computation strategies – some exponentially faster, some simultaneous – that are 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 computation to occur.
While experimenting with different geometrical combinations of devices just billionths of a meter in size that control quantum dots, and various types of miniscule magnets and antennas that drive their operations, the researchers stumbled across a strange effect.
“I was trying to really accurately operate a two-qubit gate,” says Dr. Tanttu, an engineer at Diraq, “iterating through a lot of different devices and slightly different geometries. 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 before.”
This discovery, the engineers realized, was a new way of manipulating the quantum state of a single qubit by using electric fields, rather than the magnetic fields used previously. Since this discovery in 2020, the researchers have been perfecting the technique – which has become another tool in their arsenal to fulfil Diraq’s ambition of building billions of qubits on a single chip.
“This is a new way to manipulate qubits,” says Gilbert, “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. There’s less clutter.”
Prof Andrew Dzurak, CEO and Founder of Diraq, and Professor in Quantum Engineering at UNSW adds, “[This] 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 is 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.”
For more, see “On-demand electrical control of spin qubits.”
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