Google Reduces Magic State Errors by 40x on the Willow Processor

ChainCatcher report: The Google Quantum AI team published a paper in Science, announcing that their "magic state cultivation" technique on the Willow processor reduced errors by approximately 40-fold, producing T states with logical fidelity of 99.99%. Magic states are one-time resources required to run useful quantum programs and are consumed upon each use; according to Google’s estimates, producing magic states can account for up to 95% of a quantum computer’s total capacity, leaving very limited resources for actual computation. The previous standard approach, magic state distillation, proposed by physicists Sergei Bravyi and Alexei Kitaev in 2004, requires a large number of qubits dedicated solely to this task. In 2024, Google researchers introduced a more cost-effective cultivation method that functions more like a filter: injecting rough magic states into a small region of the chip, running a series of checks to eliminate all defective attempts, and allowing successful ones to gradually amplify. In the experiment, only about 8% of attempts passed all checks—meaning over 90% of attempts were discarded to preserve each clean state. This cultivation technique is one of the foundations for Gidney’s 2025 estimate that RSA-2048 encryption could be broken by fewer than one million noisy qubits—a 20-fold improvement over his 2019 estimate of 20 million qubits. This experiment used at most 54 of Willow’s 105 qubits; the paper notes that factoring an RSA-2048 key requires magic states with an error rate of about one in ten billion—roughly a million times cleaner than the results achieved here.