Google stated that its Willow quantum processor diminished errors roughly 40 times over when creating “magic states,” an essential resource for quantum computations that could eventually pose a hazard to Bitcoin wallets.
The test achieved about 99.99 percent fidelity among the states that cleared inspection, although merely about 8 percent of preparation tries succeeded and major scaling obstacles still persist.
These outcomes do not render a Bitcoin breach 40 times cheaper, but they progress an engineering technique that might assist future quantum computers in sustaining the roughly 500,000 dependable magic states per second demanded under a specific modeled assault.
Google reports that its Willow quantum chip has slashed errors around 40-fold when generating specialized states utilized in quantum processing, confronting an expensive milestone toward building processors robust enough to compromise bitcoin wallets.
This outcome, released in Science this week, addresses a factor that infrequently surfaces in the bitcoin quantum debate—which generally concentrates on how massive a machine an adversary would require while ignoring how much of that hardware would be occupied preparing to compute.
Why the earliest coins grant an adversary extra time
A bitcoin wallet employs a private key to authorize transactions and a matching public key that allows the network to verify those authorizations. Disbursing funds typically reveals the public key, whereas certain transaction formats expose it from the outset.
Working backward from the public key to the private key is meant to require an unfeasible amount of computing, which renders it practically impossible to reverse-engineer cryptocurrency wallets.
Nonetheless, a sufficiently robust quantum computer operating Shor’s algorithm could theoretically execute that math. Whoever retrieved the secret key could sign transactions as the lawful owner, and the network would accept them as valid. Mathematician Peter Shor initially published this method in 1994, but no one has yet succeeded in demonstrating it.
A recovery phrase stored inside a physical drawer grants zero defense against that threat, because the attacker would be working from data already residing on the blockchain.
Certain newer transaction formats conceal the public key behind a hash, which is a digital fingerprint, until the owner spends the funds. An assailant targeting a previously hidden key would have to wait for that exposure and might need to recover the secret quickly enough to disrupt the transfer.
That also explains why lost coins present a complex dilemma. Bitcoin can adopt stronger spending protections, but someone must still possess the active keys to migrate legacy holdings into them. If those keys are misplaced, the owner cannot execute the transfer. The exposed public key remains accessible to a future attacker.
Some of bitcoin’s oldest holdings have had their public keys exposed ever since they were minted.
Legacy coins have additionally been shifting as discussions around quantum threats intensify. On Oct. 7, 100.02 BTC untouched since July 2010 moved after more than 16 years, holding a value of approximately $8.5 million. In August, six wallets dormant since 2011–2014 transferred another 553.59 BTC, worth roughly $40 million at the time.
These transactions do not definitively prove that owners are reacting to quantum anxieties, as shifting coins can just as easily indicate changing wallets, reorganizing holdings, or getting ready to sell.
The expense of preparation
Quantum computers retain data within units called qubits, which are exceptionally fragile. Thermal energy, physical vibration, and stray signals can disrupt them and introduce errors, while incorporating additional qubits simultaneously introduces more avenues for mistakes.
Engineers manage this by organizing numerous physical qubits into clusters that detect and rectify errors. Each cluster functions as a more reliable unit, designated as a logical qubit.
These units subsequently demand the digital counterpart of fuel to execute specific operations, specifically prepared quantum states that investigators label “magic states.” Each one is consumed upon usage, meaning the computer must continuously generate them throughout a calculation.
Read More: A simple explainer on what quantum computing actually is, and why it is terrifying for bitcoin
Imagine a restaurant kitchen where every dish requires a fresh preparation of a sauce that cannot be reused, meaning a portion of the staff must continuously produce sauce while the others cook. Inside a quantum computer, hardware dedicated to generating magic states is hardware that cannot be allocated to alternative tasks.
Google’s technique, termed cultivation, begins with a crude version of the state, inspects it for flaws, and discards defective attempts. The objective is to yield clean states utilizing less hardware than previous methods required.
The company announced roughly 99.99% fidelity, which serves as a metric for how precisely the final states aligned with what the scientists intended to create.
That figure applies exclusively to the states that successfully cleared inspection. Willow retained approximately 8% of its trials following the evaluations conducted during generation and measurement. Out of every 100 tries, around eight successfully passed.
Subsequent phases involve executing the procedure at a vastly expanded scale and maintaining the usefulness of those states as they feed into extended calculations. The researchers indicate that further labor is required regarding real-time operations and transitioning the states into more robust error-correcting configurations.
Google kept 8 in 100 tries, and those 8 were near-perfect. (Shaurya Malwa/CoinDesk)
How this aligns with prior research
In March, Google projected that an upcoming superconducting quantum processor possessing fewer than 500,000 physical qubits could crack the wallet cryptography utilized by Bitcoin and Ethereum, under a specific set of hardware assumptions.
In September, CoinDesk covered researchers reducing the computational load of a core calculation deployed within that assault. That study addressed a single component, omitting the complete attack and the physical hardware expenses associated with running it.
Those investigations diminish the volume of math an adversary must perform. Cultivation tackles the expense of supplying the hardware while it computes that math.
These efficiency gains cannot simply be multiplied together. Google’s March forecast already presumed efficient magic-state generation. The experiment evaluates a portion of that engineering framework, instead of delivering another 40-fold decrease in the projected cost of attacking bitcoin.
The March whitepaper additionally illustrates the quantity of fuel such an attack would consume. For a single modeled assault persisting for roughly nine minutes following the appearance of a public key, Google estimated the processor would demand approximately 500,000 adequately reliable magic states every second.
Originally published at https://www.coindesk.com/tech/2026/10/16/satoshi-era-bitcoin-faces-a-bigger-quantum-threat-after-google-s-new-willow-breakthrough.
