Australian researchers have proven that near error-free quantum computing is possible. 

Quantum computing in silicon hit 99 per cent accuracy in recent UNSW-led research. The breakthrough paves the way for large silicon-based quantum processors for real-world manufacturing and application.

“Today’s publication in Nature shows our operations were 99 per cent error-free,” says Professor Andrea Morello, who led the work.

“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.”

“This piece of research is an important milestone on the journey that will get us there.”

Prof Morello’s paper is one of three published in the same journal that each independently confirm that robust, reliable quantum computing in silicon is now a reality.

Prof Morello’s team achieved 1-qubit operation fidelities up to 99.95 per cent, and 2-qubit fidelity of 99.37 per cent with a three-qubit system comprising an electron and two phosphorous atoms, introduced in silicon via ion implantation.

In a second paper, a Delft team in the Netherlands achieved 99.87 per cent 1-qubit and 99.65 per cent 2-qubit fidelities using electron spins in quantum dots formed in a stack of silicon and silicon-germanium alloy (Si/SiGe).

Separately, a RIKEN team in Japan achieved 99.84 per cent 1-qubit and 99.51 per cent 2-qubit fidelities in a two-electron system using Si/SiGe quantum dots.

The UNSW and Delft teams certified the performance of their quantum processors using a sophisticated method called gate set tomography. 

The UNSW has shown that it can preserve quantum information in silicon for 35 seconds.

“In the quantum world, 35 seconds is an eternity,” says Prof Morello. 

“To give a comparison, in the famous Google and IBM superconducting quantum computers the lifetime is about a hundred microseconds – nearly a million times shorter.”

The trade-off was that isolating the qubits made it seemingly impossible for them to interact with each other, as necessary to perform actual computations. However, the new paper describes how the team overcame this problem by using 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 Dr 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.”

“This really is an unlocking technology,” says Dr Serwan Asaad, another lead experimental 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.”