Quantum future: computing in silicon hits 99% accuracy

Researchers at the University of New South Wales (UNSW) have proven that near error-free quantum computing is possible, a key step in the road to building silicon-based quantum computers, the processors of the future.

“Today’s publication in Nature shows our operations were 99% error-free,” says UNSW’s Andrea Morello, lead author of the research.

“When the errors are so rare, it becomes possible to detect them and correct them when they occur. This shows that it is possible to build quantum computers that have enough scale, and enough power, to handle meaningful computation.”

What’s the deal with quantum computers?

Quantum computers – when they become a practicable reality – will convey information through “spin”, the property of an electron or atom that gives it magnetism. The unit of spin is a qubit. Traditional computers, on the other hand, convey information via electrical charges.

Quantum computers have such revolutionary potential because they’re not simply faster processors than traditional computers, they actually harness entirely different laws of physics.

Where regular computers adhere to strict rules of logic, quantum objects – objects at a tiny scale, like electrons – can challenge the traditional laws of physics. A quantum object can be isolated in a quantum state so it conveys two things at once, like a 0 and a 1.

Quantum computers will be particularly useful for crunching huge numbers; that’s why it’s thought they’ll be able to revolutionise all sorts of fields, from helping to create new medicines through to pricing financial instruments.

But the road to quantum computing is paved with complex problems, and solving these has been a hallmark of UNSW’s quantum researchers. Previously, Morello has demonstrated the preservation of quantum information in silicon for 35 seconds which, “in the quantum world … is an eternity”. And just last August, UNSW scientists Jarryd Pla and Andrew Dzurak announced they had solved the problem of attempting to control electron spin qubits, a necessary step to scaling quantum processors.

So, how did they do it?

This new breakthrough addresses a key quantum conundrum; isolating qubits to preserve the information they contained made it seemingly impossible for them to interact with one another, in order to perform actual computations.

So, the research team used an electron encompassing two nuclei of phosphorus atoms.

“If you have two nuclei that are connected to the same electron, you can make them do a quantum operation,” says Mateusz Mądzik, one of the lead experimental authors.

“While you don’t operate the electron, those nuclei safely store their quantum information. But now you have the option of making them talk to each other via the electron, to realise universal quantum operations that can be adapted to any computational problem.”

The new technology could be a key stepping stone in the progress to a fully functioning quantum computer.

“This really is an unlocking technology,” says Serwan Asaad, another lead author. “The nuclear spins are the core quantum processor. If you entangle them with the electron, then the electron can then be moved to another place and entangled with other qubit nuclei further afield, opening the way to making large arrays of qubits capable of robust and useful computations.”

And the team say their technology is compatible with the existing computing industry, because the method used to introduce the phosphorus atoms into the silicon chip is already used to make traditional silicon computer chips.

While all existing computers deploy error correction, the laws of quantum physics pose restrictions on how correction can take place in a quantum computer. Using this new technology, however, the team were able to produce stunningly accurate results, with their operations 99% error-free.

A bonzer day for quantum computing

The UNSW study is one of three published today in Nature that independently show robust, reliable quantum computing is inching closer.

A team from the Delft University of Technology in the Netherlands, led by Lieven Vandersypen, and a team from RIKEN in Japan achieved similarly error-free results.

Spin qubits in silicon are poised to be the platform of choice for reliable quantum computers. They are stable enough to hold quantum information for long periods and can be scaled up using techniques the computer industry is already well acquainted with.

“Until now, however, the challenge has been performing quantum logic operations with sufficiently high accuracy,” says Morello.

“Each of the three papers published today shows how this challenge can be overcome to such a degree that errors can be corrected faster than they appear.”