Google Quantum AI announced Thursday that a technique called magic state cultivation reduced errors by approximately 40 times on its Willow processor, producing magic states with 99.99% fidelity, according to research published in Science.
Magic states are single-use resources required to run useful quantum programs. Google cited estimates suggesting that producing magic states consumes up to 95% of a quantum computer's total processing capacity, making error reduction in this area potentially transformative for the field.
How Magic State Cultivation Works
Magic state distillation, the standard approach developed by physicists Sergei Bravyi and Alexei Kitaev in 2004, requires extensive qubit factories to produce clean states from noisy ones. Google's alternative approach, magic state cultivation, functions as a filter rather than a factory. The technique injects rough magic states into a small chip region, runs checks, discards attempts with detected flaws, and preserves the survivors.
On Willow, the protocol achieved T-states with record logical fidelity of 99.99%. However, only approximately 8% of attempts passed all checks, meaning the chip discards more than nine out of every 10 tries to retain one clean state.
Implications for Cryptography
Magic state cultivation factors into estimates about quantum computing's potential threat to encryption. Researcher Craig Gidney estimated in 2025 that RSA-2048 encryption could theoretically be broken with fewer than one million noisy qubits, down from his 2019 estimate of 20 million qubits.
A whitepaper co-authored with Ethereum Foundation researcher Justin Drake and Stanford cryptographer Dan Boneh projected that breaking Bitcoin's elliptic curve cryptography could require fewer than 500,000 physical qubits. Breaking an RSA-2048 key would require magic states with errors around one in 10 billion—approximately one million times cleaner than Google's current achievement.
Current Limitations
Google's experiment used at most 54 of Willow's 105 qubits. The company states that the next step involves running cultivation at larger scale, projecting that halving Willow's underlying hardware noise would reduce magic state errors to approximately two in 100,000, as errors in the process shrink with the cube of the chip's noise level.
