The team from UNSW Sydney (the University of New South Wales) say that their discovery will enable scaling up to a full-scale quantum processor.
In 2015 Professor Andrew Dzurak of UNSW and his team was the first to build a quantum logic gate in silicon, making calculations between two qubits of information possible - and thereby clearing a crucial hurdle to making silicon quantum computers a reality.
A number of groups around the world have since demonstrated two-qubit gates in silicon - but until now, 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," Dr Henry Yang, senior research fellow at UNSW, says.
Quantum computers will have a wide range of important applications in the future thanks to their ability to perform far more complex calculations at much greater speeds, including solving problems that are simply beyond the ability of today's computers. However, for that to be possible, millions of qubits will be needed, meaning that even the smallest of quantum errors will need to be corrected.
"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," explains Prof. Dzuark.
"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."
In this study, the team implemented and performed Clifford-based fidelity benchmarking - a technique that can assess qubit accuracy across all technology platforms - demonstrating an average two-qubit gate fidelity of 98%.
"We achieved such a high fidelity by characterising and mitigating primary error sources, thus improving gate fidelities to the point where randomised benchmarking sequences of significant length - more than 50 gate operations - could be performed on our two-qubit device," says Wister Huang, the lead author on the paper.
The researchers say the study is further proof that silicon as a technology platform is ideal for scaling up to the large numbers of qubits needed for universal quantum computing.
"If our fidelity value had been too low, it would have meant serious problems for the future of silicon quantum computing. 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," Prof Dzurak says.
"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."
