Google's quantum chip cuts magic-state errors 40-fold, hits 99.99% fidelity

Google's Willow quantum processor has reduced errors in preparing specialized "magic states" by 40-fold, achieving 99.99% logical fidelity, a key step toward practical quantum computing. The technique, called magic state cultivation, filters out errors through coordinated measurements, discarding failed attempts to produce cleaner states. These states are vital for complex calculations but previously consumed up to 95% of a quantum computer's capacity, as each can only be used once. Google researchers improved processor controls and developed a new benchmarking method after tracing noise to lab equipment drift. The team also successfully transferred purified states between two error-correction codes, though scaling remains a major challenge before fault-tolerant quantum computers become viable.