Google Quantum AI researchers say they have achieved a major milestone in quantum computing by demonstrating a logical qubit with 99.5% fidelity in a new preprint released Friday. The result suggests the company has moved closer to building systems that can correct errors more effectively than individual physical qubits alone.

A logical qubit is formed by combining multiple physical qubits to store and process information in a way that is less vulnerable to noise and instability. That kind of error correction is widely seen as essential if quantum computers are ever to become reliable enough for practical use at scale.

According to the researchers, the reported error rates fall below the threshold of the physical qubits used in the experiment, a key sign that the approach may be able to improve as systems grow larger. While the work is still at the research stage, it adds to growing competition among major technology firms pursuing fault-tolerant quantum hardware.

Even with this progress, experts caution that large-scale quantum computing remains a difficult engineering problem. The new result does not mean a commercial quantum computer is around the corner, but it does represent a notable advance in the long effort to make quantum machines more stable and useful.