Google’s Willow chip shows ‘magic state cultivation,’ cutting errors 40x as crypto watches Q-day

Summary

Google Quantum AI said a technique called magic state cultivation cut errors about 40-fold on its Willow processor and produced T-states with 99.99% logical fidelity, Decrypt and The Block reported after a Science paper published Thursday.

Decrypt said magic states are scarce resources for useful quantum programs and that some estimates put making them at up to 95% of a machine’s capacity; Google framed cultivation as a cheaper filter-style alternative to large distillation factories.

Both outlets linked the work to longer-term encryption risk: Decrypt noted cultivation underpins estimates that RSA-2048 could fall with under a million noisy qubits, while stressing the experiment used at most 54 of Willow’s 105 qubits and is far from wallet-breaking scale.

The Block cited observers including Nic Carter saying there is no imminent threat but that AI is accelerating quantum progress, and Project Eleven’s Alex Pruden saying the result mainly validates assumptions already baked into Q-day timelines.

CoinDesk added that the 99.99% figure covers only the roughly 8% of attempts that passed inspection, and said the result does not make a Bitcoin attack 40 times cheaper because Google’s earlier attack estimates already assumed efficient magic-state production.

Updates

• Update, Sat, 17 Oct 2026 04:07:13 UTC: Added CoinDesk’s Oct. 16 analysis: only about 8% of Willow’s preparation attempts passed inspection, and CoinDesk says the result tests part of an engineering approach Google’s earlier attack estimates already assumed rather than making a Bitcoin attack 40 times cheaper.

Key facts

• Magic state cultivation on Willow cut errors about 40-fold and reached 99.99% T-state logical fidelity. (Decrypt)
• Some estimates put magic-state production at up to 95% of a quantum computer’s capacity. (The Block)
• Decrypt said the experiment used at most 54 of Willow’s 105 qubits and that breaking RSA-2048 would need far lower error rates. (Decrypt)
• The Block reported Coinbase this week urged Bitcoin post-quantum preparation as a multi-year process. (The Block)
• CoinDesk said the roughly 99.99% fidelity applies only to states that passed inspection, and that Willow kept about 8% of its preparation attempts, about eight in every 100. (CoinDesk)
• CoinDesk said the findings do not make a Bitcoin attack 40 times cheaper, because Google’s March estimate already assumed efficient magic-state production. (CoinDesk)
• CoinDesk said Google estimated in March that a future superconducting quantum computer with fewer than 500,000 physical qubits could break the wallet cryptography used by Bitcoin and Ethereum, under specific hardware assumptions, and that one modeled attack lasting about nine minutes would need roughly 500,000 sufficiently reliable magic states every second. (CoinDesk)
• CoinDesk reported that on Oct. 7, 100.02 BTC untouched since July 2010 moved, worth about $8.5 million, while noting such transfers do not on their own show holders are reacting to quantum fears. (CoinDesk)

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