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Prediction market on metaculus. In December 2024, Google [announced](https://research.google/blog/making-quantum-error-correction-work/) Willow, a 105-qubit superconducting quantum processor. Willow ran quantum error correction in the regime where adding more physical qubits to a logical qubit improves the logical qubit's reliability. Above a certain physical-qubit error rate (the threshold), adding more qubits has the opposite effect. As Google increased the surface code distance from 3 to 5 to 7, the logical error rate per cycle dropped by a factor of about 2.14 each time. This was the first peer-reviewed demonstration of scaling-with-distance error suppression on real quantum hardware. The result was published in Nature 638:920 ([Acharya et al., 2025](https://doi.org/10.1038/s41586-024-08449-y)). As of May 2026, several non-superconducting teams have published nearby results. [Harvard](https://thequantuminsider.com/2025/11/21/harvard-quantum-error-correction/) and [QuEra](https://www.nature.com/articles/s41586-023-06927-3) have shown logical-qubit operations on neutral-atom platforms with hundreds of atoms. [Quantinuum](https://spectrum.ieee.org/quantinuum-fault-tolerant-quantum-computing) has shown a fault-tolerant non-Clifford gate on a trapped-ion system. None of these has clearly met the criteria of this question (Λ > 1 across two distinct code distances on the same fixed device) in a peer-reviewed journal.
Resolves: 1/1/2029.