Google reports 40-fold error reduction in Willow quantum experiment

Google Quantum AI said on October 15, 2026, that it had demonstrated “magic state cultivation” on its Willow processor, reducing errors about 40-fold compared with states prepared without the technique. It also reported a logical fidelity of 99.99% for the T-states it produced.

Getting a trustworthy measurement was itself part of the work. According to Google, early results appeared to defy physics. The team eventually traced the problem to electrical equipment drift and temperature variation, which invalidated an assumption in its usual benchmarking method. Researchers added controls to reduce the noise and developed a new benchmark that uses cultivation to measure itself.

Magic states supply operations needed for universal, error-corrected quantum computing. They are consumed when used, and preparing sufficiently clean ones can take substantial computing resources. The aim of cultivation is to reduce that preparation cost—not simply to make an individual physical qubit less error-prone.

Google’s researchers developed the cultivation approach in 2024, building on an earlier idea. It starts with a noisy state in a small region of a quantum chip. Coordinated measurements check for errors, and flawed attempts are discarded, leaving a cleaner state that can be adapted into a larger encoding. The Willow experiment puts that filtering approach into hardware.

The team also reported transferring states from a distance-3 color code to a distance-5 surface code. These are different quantum error-correction schemes; Google describes the transfer as evidence that cultivated states can survive the move into another encoding within its architecture.

Google says the research was published in Science on October 15. This account draws on the company’s blog post, not a review of that paper. The company also identifies a substantial remaining task: demonstrating cultivation at a larger scale before it becomes realistic for practical quantum computing. The reported result is a hardware demonstration of the technique, not a demonstration of a complete, useful fault-tolerant computer.