Quantum computing in silicon hits 99% accuracy and smashes barrier

Professor Andrea Morello of UNSW

A Sydney UNSW-led team have smashed a quantum computing barrier, creating a silicon-based device with better than 99% accuracy. The research was published in Nature.

They proved that near error-free quantum computing is possible, paving the way to build silicon quantum devices compatible with current semiconductor manufacturing technology.

“The publication shows 99% error-free,” says Professor Andrea Morello of UNSW, who led the work, with partners in the US, Japan, Egypt, UTS and the University of Melbourne.

“When the errors are so rare, it is possible to detect 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 says.

Quantum computing in silicon hits the 99% threshold

Morello’s paper is one of three published in Nature that independently confirm that robust, reliable quantum computing in silicon is now a reality and features on the front cover.

  • Morello et al achieved 1-qubit operation fidelities up to 99.95%, and 2-qubit fidelity of 99.37% with a three-qubit system comprising an electron and two phosphorous atoms, introduced in silicon via ion implantation.
  • A Delft team in the Netherlands led by Lieven Vandersypen achieved 99.87% 1-qubit and 99.65% 2-qubit fidelities using electron spins in quantum dots formed in a stack of silicon and silicon-germanium alloy (Si/SiGe).
  • A RIKEN team in Japan led by Seigo Tarucha similarly achieved 99.84% 1-qubit and 99.51% 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, developed at Sandia National Laboratories in the U.S. and made openly available to the research community.

Morello had previously demonstrated that he could preserve quantum information in silicon for 35 seconds, due to the extreme isolation of nuclear spins from their environment.

“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.”

But 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.

Nuclear spins learn to interact accurately

They overcame 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, a 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.”

David Jamieson, research leader at the University of Melbourne, expounded on the aspect.

“The phosphorous atoms were introduced in the silicon chip using ion implantation, the same method used in all existing silicon computer chips. This ensures that our quantum breakthrough is compatible with the broader semiconductor industry.”

Computers deploy some error correction and data redundancy, but the laws of quantum physics pose restrictions on how the correction takes place in a quantum computer.

Prof. Morello explains further, saying, “You typically need error rates below 1%, to apply quantum error correction protocols. Having now achieved this goal, we can start designing silicon quantum processors that scale up and operate reliably for useful calculations.”