Satoshi-era bitcoin faces a bigger quantum threat after Google’s new Willow breakthrough

The firm reported about 99.99% fidelity, a measure of how closely the finished states matched what researchers were aiming for.

That number applies only to the states that passed inspection. Willow kept about 8% of its attempts after the checks during preparation and measurement. For every 100 tries, about eight made it through.

The next steps include running the process at a much larger scale and keeping those states useful as they feed into longer calculations. The researchers say more work is needed on real-time operations and moving the states into stronger error-correcting setups.

How it fits with earlier research

In March, Google estimated that a future superconducting quantum computer with fewer than 500,000 physical qubits could break the wallet cryptography used by Bitcoin and Ethereum, under a specific set of hardware assumptions.

In September, CoinDesk reported on researchers cutting the workload of a core calculation used in that attack. That work covered one component, leaving out the complete attack and the physical hardware costs of running it.

Those studies reduce the amount of math an attacker has to do. Cultivation addresses the cost of supplying the machine while it does that math.

The gains cannot simply be multiplied together. Google’s March estimate already assumed efficient magic-state production. The experiment tests part of that engineering approach, rather than providing another 40-fold reduction in the estimated cost of attacking bitcoin.