Google’s Willow quantum chip reduced errors about 40-fold when preparing special states used in quantum calculations, according to results published in Science this week. The work addresses a costly step toward building machines powerful enough to break bitcoin wallets.
It does not mean bitcoin is broken now. It does mean the preparation overhead deserves more attention.
Why preparation time matters
Much of the bitcoin quantum debate asks how large a machine an attacker would need. That focus misses another question: how much of the machine would be tied up getting ready to calculate. Willow’s error reduction is a step on that path. The result is about state preparation, not a demonstrated attack on bitcoin.
How exposed keys change the clock
A bitcoin wallet uses a secret key to approve payments and a matching public key so the network can check them. Spending usually reveals the public key. Some payment types expose it from the start. Working backward from the public key to the secret key is meant to be impractical. A large enough quantum computer running Shor’s algorithm could, in theory, do the math. Whoever recovered the key could sign transactions as the owner, and the network would accept them. Shor published the method in 1994. No one has demonstrated it.
A recovery phrase in a drawer does not help against this kind of attack. The attacker would work from information already on the blockchain. Later payment formats hide the public key behind a hash until the owner spends. An attacker targeting a previously hidden key would need to wait for exposure and then recover the secret fast enough to interfere with the payment.
Lost coins and old wallets
Lost coins are a hard case. Bitcoin can add stronger spending protections, but someone still needs existing keys to move old holdings into them. If keys are lost, the owner cannot move the coins. The exposed public key stays available to a future attacker. Some of bitcoin’s oldest holdings have had public keys exposed since they were mined.
Old coins have also been moving as the quantum debate gets louder. On Oct. 7, 100.02 BTC untouched since July 2010 moved after more than 16 years, worth about $8.5 million. In August, six wallets inactive since 2011-2014 moved 553.59 BTC, worth roughly $40 million at the time. Those transfers do not prove holders are reacting to quantum fears. Moving coins can mean changing wallets, reorganizing holdings, or preparing to sell.
