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

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 where any calculation is safe from errors.

Any operation of a quantum computer can be broken into simpler operations called quantum gates. Applying a quantum gate to a qubit consists of changing its quantum state by hitting it with a laser . The team 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 7 entangled ions. Two more qubits served as “flags” that let the computer know when some erroneous computation needs 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 team demonstrated that each of the logic gates within their system works, reducing the errors.

While this setup may be useful for certain types of quantum computers, the difficulty in programming error correction into these devices significantly varies among quantum computer designs, says Christopher Monroe at the Joint Quantum Institute. 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 colleagues used 13 trapped ions to build a single logical qubit that stored data unexpectedly accurately also thanks to error correction.

He says this new quantum computer is not yet big enough 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.”

### Reference:

Philipp Schindler et al, Demonstration of fault-tolerant universal quantum gate operations, Nature (2022). DOI: 10.1038/s41586-022-04721-1

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Physics