A quantum computer could catch its own errors on any calculation

A set of 16 qubits has been arranged so that they may be able to run any calculation error-free – a crucial step toward building quantum computers that can outpace traditional ones

By Karmela Padavic-Callaghan

A view inside the device that trapped ions

Matthias Brandl/University of Innsbruck via Institute for Experimental Physics

A quantum computer made of charged atoms can catch its own errors when performing any operation – a meaningful step towards more reliable and practical quantum computers.

Conventional computers routinely flag and correct their own errors, so to truly outperform them, quantum computers will have to do the same. However, quantum effects can make errors cascade quickly through the qubits, or quantum bits, that make up these devices.

Lukas Postler at the University of Innsbruck in Austria and his colleagues have now built a quantum computer that runs any calculation without errors.

Any operation of a quantum computer can be broken down into simpler computations called quantum gates. These can be applied to a qubit by hitting it with a laser to change its quantum state. The researchers created a set of gates that are necessary building blocks for more complicated computations and that keep even the most complex of them error-free.

They used electric fields to trap 14 calcium ions in place, forming two so-called logical qubits, each made of seven entangled ions. Two more qubits served as “flags” that let the computer know when some erroneous computation needed to be corrected.

“With this universal set of gates, you can approximate every calculation that you can possibly want to do with a quantum computer,” says Postler. The researchers demonstrated that each of the logic gates within their system works, reducing the errors.

While this set-up may be useful for certain types of quantum computers, it might not work for more complicated systems, says Christopher Monroe at the Joint Quantum Institute in Maryland. The difficulty in programming error correction into quantum computers varies significantly between devices. For quantum computers that use superconducting qubits, such as Google’s Sycamore, error correction from the get-go requires devices much larger than 16 qubits, he says.

In 2021, Monroe and his colleagues used 13 trapped ions to build a single logical qubit that stored data unexpectedly accurately because of error correction.

He says the new quantum computer isn’t yet big or reliable enough to tackle any practical real-world problem.

“Different research groups are putting the pieces together on how to do that with trapped ion qubits,” he says. “This new experiment is another piece of that puzzle.”

Journal reference: Nature, DOI: 10.1038/s41586-022-04721-1