A research team from Google Quantum AI, the Ethereum Foundation, and Stanford published a paper on March 30, 2026, detailing optimized quantum circuits. These circuits target the ECDLP-256 problem and the secp256k1 elliptic curve, which secure Bitcoin and Ethereum.
The study estimates that fewer than 500,000 physical superconducting qubits are required to break this cryptography, a 20-fold reduction from previous estimates of 9 million. Two circuit variants were proposed: one using 1,200 logical qubits and 90 million Toffoli gates, and another using 1,450 logical qubits and 70 million Toffoli gates.
Execution times for these circuits range from 9 to 23 minutes. A separate study by Caltech and Oratomic researchers suggests that neutral-atom architectures could potentially require between 10,000 and 26,000 physical qubits, though these systems would require days to complete the computation.
The paper identifies two attack vectors: an 'on-spend' attack, which targets transactions during the 10-minute confirmation window with an estimated 41% success probability, and an 'at-rest' attack targeting wallets with exposed public keys.
Approximately 6.9 million BTC and 20.5 million ETH are currently vulnerable to at-rest attacks. Additionally, administrative keys for smart contracts governing assets worth $200 billion are identified as a potential vulnerability.
Currently, no quantum computer reaches the 500,000 physical qubit threshold; Google’s Willow processor operates with 105 qubits. Researchers recommend using fresh addresses for every transaction to mitigate risks.
