A FRENCH QUANTUM LAB PUTS BITCOIN’S CURVE AT 30,000 CAT QUBITS AND ONE HOUR — 17 TIMES FEWER THAN GOOGLE’S MARCH FIGURE — IF ITS QUBITS NEVER BIT-FLIP
On October 28, 2026, ten researchers, nine of them at the French quantum startup Alice & Bob, posted a preprint to the IACR ePrint archive, paper 2026/2665. Its abstract says that solving the discrete log on secp256k1, the curve bitcoin keys use, “requires at most 30 000 cat qubits and 1 hour.” The Quantum Insider, reporting the company’s release on October 29, gives the exact figures as 29,588 qubits and 61.8 minutes. Google Quantum AI’s March 30 paper put the same job at fewer than half a million physical qubits. That gap is the 17 times in CoinDesk’s headline: 500,000 divided by 29,588 is 16.9.
Read the conditions before the number. The abstract assumes a 1 microsecond error correction cycle, phase-flip noise of 5 in 10,000, and no bit-flips at all. The authors say no bit-flips means a qubit that holds its bit for about 100 years. Relax that to about one hour and their RSA-2048 count rises from about 23,000 to about 45,000 qubits. The abstract gives no bitcoin figure for that relaxed case. Google’s paper assumed ordinary qubits with an error rate of 1 in 1,000. The two designs do not rest on the same hardware, so the 17 is a comparison of blueprints.
The clock matters as much as the count. Google estimated about 9 to 23 minutes per key, close to one block. Alice & Bob’s design takes about an hour, roughly six blocks. A payment waiting in the mempool would most likely confirm before this machine finished. The coins it would reach are the ones whose public keys already sit on chain: old pay-to-public-key outputs, reused addresses and taproot outputs. Our September 20 piece covered how many coins sit that way and how far the fixes were from done.
What you can check: the preprint is public, under a CC BY license, and it names the curve. What you cannot check is the machine, because it does not exist. Until someone runs cat qubits that hold for a very long run, 30,000 is a design target, not a result. The target keeps getting smaller, and coins with exposed keys are the ones it points at first. At the time of this writing, bitcoin was $81,436.