A Princeton discovery in quantum computing shows promise for silicon ‘qubits’

A discovery by Princeton physicists paves the way for silicon-based technologies in quantum computing, especially as quantum bits – the basic units of quantum computers.

Why it’s important: Silicon is a naturally abundant element, so it’s found in everyday materials, from sand to computer chips. But as much as manufacturers are eager to build quantum bits from silicon, science hasn’t caught up yet. Instead, some large companies have built their computers based on superconducting qubits, which are short-lived and extremely large. Silicon qubits are long-lasting and could be more easily mass-produced, but until now, silicon qubits have been a bit of an underdog technology.

Perhaps they are finally getting their day through the work of Jason Petta’s group and others in this field, said Adam Mills, a graduate student in Petta’s lab at Princeton University’s Department of Physics and the lead author of a recently published paper in the journal Science Advances. “It looks like a big year for silicon in general.”

Using a silicon device called a double quantum dot, Petta, Mills and their team successfully captured two electrons and forced them to interact, resulting in an unprecedented level of fidelity: over 99.8 percent, comparable to the best results achieved by competing technologies. (Fidelity, a measure of a qubit’s ability to perform error-free operations, is a key feature in the quest for practical and efficient quantum computers.)

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

In general, silicon spin qubits have advantages over other qubit types, Mills said. “Every system will have to scale up to many qubits,” he said. “And right now the other qubit systems have real physical limitations to scalability. Size can 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 of single electrons and are extremely small.

“Our devices are only about 100 nanometers in diameter, while a conventional superconducting qubit is about 300 microns in diameter, so if you want to make a lot of them on a chip, it becomes difficult to use a superconducting approach,” Petta says. , the Eugene Higgins Professor of Physics at Princeton and the senior author of the article. There are 1,000 nanometers in one micron (micrometer), so the 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 make a million or 10 million qubits needed to do something practical, that’s only going to happen in a solid-state system that can be scaled using the standard semiconductor fabrication industry.”

Read the full story on the website of the Department of Physics.

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