John M. Martinis (존 M. 마티니스), a Nobel Prize-winning physicist who led development of Google's quantum computers, named Bitcoin (BTC) as one of the early real-world targets for quantum computers and stressed the need for pre-emptive action.

On April 7 local time, blockchain media outlet CoinDesk reported that Martinis recently said a scenario in which a quantum computer could crack Bitcoin cryptography in minutes should not be dismissed as merely hypothetical, as outlined by Google researchers.

Martinis described Google's related paper as "a very well-written paper" that shows where things stand now. "This is not something with a probability of zero," he said. "People need to address this issue."

The core of the Google paper is that a sufficiently advanced quantum computer could derive a private key from a Bitcoin public key, sharply lowering the computational barrier that supports the current network. Martinis called it "one of the issues that must be taken most seriously."

He particularly saw codebreaking becoming practical in quantum computing sooner than expected. "Breaking cryptography is one of the easier applications in quantum computing because it is numbers-based," he said, describing it as so-called "low-hanging fruit." He also said the elliptic curve cryptography structure used by Bitcoin could fall within the scope of such attacks.

On the response side, he said Bitcoin is more complex than traditional financial systems. Centralised systems such as banks can transition to quantum-resistant cryptography, but Bitcoin's decentralised network means upgrades take time and require community consensus. "Bitcoin is structurally different, so we need to start discussions now," he said.

He cited the period immediately after a transaction is propagated as a specific risk window. A "time window" exists after a transaction is sent to the network and before it is included in a block, when the public key is exposed. During that period, he said, a powerful quantum computer could potentially infer the private key and steal funds.

He did not, however, say the threat would immediately become reality. "Quantum computers will be harder to build than people think," Martinis said, citing major engineering challenges including scalability, reliability and error correction. He went on to mention roughly 5 to 10 years for the arrival of a quantum machine that is meaningful for cryptography, but repeatedly stressed the need to prepare now given the magnitude of the consequences.