File: 9 October 2026 · Source date: 9 October 2026
Why is error inevitable?
Qubits lose information due to interaction with the environment, control defects and measurement errors. Quantum error correction aims to measure and correct errors by distributing the information of a logical qubit to a large number of physical qubits.
Sub-threshold study
If the physical error rate in the surface code is below the critical threshold, the logical error rate is expected to decrease as the code distance increases. Published with Willow processors, the study showed that larger code improves logical memory and subthreshold behavior with real-time analysis.
Why not a finished computer?
This result does not mean that the large-scale fault-tolerant quantum computer is complete. Rare associated errors, hardware cost, long algorithms, and fast classical resolution are still core issues.
discussion question
When evaluating progress in a quantum computer, is the number of qubits or the logical error rate more significant?
Resources and further reading
Nature — Quantum error correction below the surface code threshold ↗Google Quantum AI — Willow ↗Share your answer
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