Google says it has shown, for the first time, a practical solution to one of quantum computing’s biggest hurdles. The method cut errors about 40-fold on its Willow chip in research published in Science on October 15.
Quantum computers are a new kind of machine that may one day crack the codes protecting Bitcoin (BTC). Today’s machines are far too small for that. Google says its method could reduce how big future machines need to be.
How Google Grew a Cleaner Quantum Ingredient
To run useful programs, a quantum computer needs certain operations, which it builds from special ingredients called magic states. Google said some estimates suggest making clean ones could take up to 95% of a machine’s capacity.
Google’s method, called magic state cultivation, works by elimination. The chip starts with a rough, error-prone state, runs a series of checks, and discards every failed attempt. What survives grows into a much cleaner state.
On Willow, cultivated states had about 40 times fewer errors than those made without the method. They reached what Google called a record 99.99% fidelity, a measure of accuracy.
If it works at larger scale, the team said, the method could substantially shrink the machine needed for practical tasks. Google has used the same measure, machine size, to estimate the threat to Bitcoin.
“This work is the first demonstration of a practical solution to one of quantum computing’s most severe resource bottlenecks. It demonstrates, on real hardware, that we can efficiently create these crucial magic states,” the blog read.
The Bitcoin Math Behind Google’s Result
A powerful enough quantum computer could, in theory, work out a wallet’s private key from its public key. In March, Google estimated that such an attack would need fewer than 500,000 qubits.
That attack also calls for tens of millions of operations that require magic states. Cultivation has already helped shrink a similar estimate. In 2025, Google researcher Craig Gidney used it to cut the machine needed to break RSA. RSA is a widely used encryption system.
Willow, Google’s current chip, has 105 qubits, far below 500,000. Google itself noted the limits of the result.
“Of course, we still need to demonstrate magic state cultivation at a larger scale to make it realistic for practical quantum computing, and plenty of technical challenges remain,” the team added.
Still, some coins would be easier to target if such a machine arrived. Glassnode data puts 6.04 million BTC, or 30.2% of all mined Bitcoin, in addresses with visible public keys. That stash is worth about $494 billion, with Bitcoin trading at $81,857, up 1.19% over the past 24 hours.
Most of those coins can still move to safer addresses. However, a June study estimated that about 2.3 million BTC cannot. They are lost, dormant, or date back to Bitcoin’s earliest days.
What happens to those stuck coins is still undecided. Coinbase called it a difficult question in an October 13 post on Bitcoin’s switch to quantum-resistant security.
The exchange listed options ranging from freezing old coins to rescue tools that let owners reclaim them. It also favored a staged approach that lets active wallets adopt quantum-resistant options early. Coinbase called the post an input to an open discussion, not a final position.
The June study estimated that a migration started in 2026 could finish between 2029 and 2031. That would beat even an optimistic 2035 arrival for a code-breaking machine. Google gave no timeline for proving its method at a larger scale.
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