UNSW claims accuracy in quantum calculations

The university's engineers have announced the capability to determine the accuracy of two-qubit calculations in silicon.

Engineers from the University of New South Wales (UNSW) have followed up on a 2015 quantum computing breakthrough, announcing that they have measured the accuracy of silicon two-quantum bit (qubit) operations for the first time.

Measuring the fidelity of two-qubit logic operations in silicon, UNSW said the results confirm the promise behind using silicon for quantum computing.

"All quantum computations can be made up of one-qubit operations and two-qubit operations -- they're the central building blocks of quantum computing," UNSW Scientia Professor Andrew Dzurak said. "Once you've got those, you can perform any computation you want -- but the accuracy of both operations needs to be very high."

There's a big race internationally to build the first quantum computer and Australia is betting on silicon.

UNSW's approach has been to focus on making qubits out of single atoms of phosphorus or quantum dots in silicon -- the material that forms the basis of today's computer chips.

Researchers from the university unlocked the key to enabling quantum computer coding in silicon in late 2015, announcing that UNSW at the time had built a quantum logic gate in silicon, making calculations between two qubits of information possible.

Read more: Australia's ambitious plan to win the quantum race

While teams around the world have since demonstrated two-qubit gates in silicon, UNSW on Tuesday said until its breakthrough, the true accuracy of such a two-qubit gate was unknown.

"Fidelity is a critical parameter which determines how viable a qubit technology is -- you can only tap into the tremendous power of quantum computing if the qubit operations are near perfect, with only tiny errors allowed," explained Dr Henry Yang, a senior research fellow at UNSW who, alongside final-year PhD student in Electrical Engineering Wister Huang, conducted the experiment.

The university said that in conducting its study, the team implemented and performed Clifford-based fidelity benchmarking, which is a technique assesses qubit accuracy across all technology platforms. The benchmarking outcome resulted in an average two-qubit gate fidelity of 98%.

Read also: What will you actually use quantum computing for?

According to Dzurak, if the team's fidelity value had been too low, it would have meant serious problems for the future of silicon quantum computing.  

"And you're going to have to correct quantum errors, even when they're small," he explained. "For error correction to be possible, the qubits themselves have to be very accurate in the first place -- so it's crucial to assess their fidelity. The more accurate your qubits, the fewer you need -- and therefore, the sooner we can ramp up the engineering and manufacturing to realise a full-scale quantum computer."

For most of the application's quantum computing promises, Dzurak said millions of qubits will be needed.  

"The fact that it is near 99% puts it in the ballpark we need, and there are excellent prospects for further improvement. Our results immediately show, as we predicted, that silicon is a viable platform for full-scale quantum computing," he said.

"We think that we'll achieve significantly higher fidelities in the near future, opening the path to full-scale, fault-tolerant quantum computation. We're now on the verge of a two-qubit accuracy that's high enough for quantum error correction."

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