Princeton discovery in quantum computing holds promise for silicon ‘qubits’

A discovery by Princeton physicists is paving the way for silicon-based technologies in quantum computing, specifically in the form of quantum bits – the basic units of quantum computers.

Why it matters: Silicon is a naturally abundant element, which is why it’s found in everyday materials, from sand to computer chips. But while manufacturers would love to build quantum bits out of silicon, science has yet to catch up. Instead, some large companies have built their computers around superconducting qubits, which don’t last as long and are extremely large. Silicon qubits are long-lasting and might be easier to mass-produce, but until now silicon qubits have been a bit of an overlooked technology.

They can finally have their day, thanks to the work of the group of Jason Petta and others in this area, said Adam Mills, a graduate student in the Petta lab in the Department of Physics at Princeton University and senior author of a recently published article in the journal Science Advances. “It looks like a big year for silicon as a whole.”

Using a silicon device called a double quantum dot, Petta, Mills and their team were able to capture two electrons and force them to interact, resulting in an unprecedented level of fidelity: greater than 99.8%, tied with the best results obtained by competing technologies. (Fidelity, which is a measure of a qubit’s ability to perform error-free operations, is a key characteristic in the quest to develop practical and efficient quantum computing.)

A qubit, in simple terms, is a quantum version of a computer bit, which is the smallest unit of data in a computer. Like its classical counterpart, the qubit is encoded with information that can have the value of one or zero. But unlike the bit, the qubit exploits the concepts of quantum mechanics, giving quantum computers a greater advantage over conventional computers, for example by factoring very large numbers or isolating the most optimal solution to a problem.

In general, silicon spin qubits have advantages over other types of qubits, Mills said. “Each system will need to scale up to many qubits,” he said. “And right now other qubit systems have real physical limits to scalability. Size could be a real issue with these systems. There’s only so much space you can cram these things into. .

In comparison, silicon spin qubits are made from single electrons and are extremely small.

“Our devices are roughly 100 nanometers in diameter, whereas a conventional superconducting qubit is more like 300 microns in diameter, so if you want to fabricate several on one chip, it will be difficult to use a superconducting approach,” said said Petta, the Eugene Higgins. Professor of physics at Princeton and lead author of the paper. There are 1,000 nanometers in a micron (micrometer), so Princeton devices are about 3,000 times smaller than their competitors.

The other advantage of silicon spin qubits, Petta added, is that conventional electronics today are based on silicon technology. “Our feeling is that if you really want to create a million or 10 million qubits that will be needed to do something practical, that’s only going to happen in a solid-state system that can be scaled up using the standard semiconductor manufacturing industry.”

Read the full story on the Department of Physics website.

Sherry J. Basler