Quantum Says 30,000 Qubits Could Break a Bitcoin Key in an Hour

The estimate assumes cat qubits that go about a century without a bit-flip, while Alice & Bob's largest demonstrator runs on a 12-qubit chip. Quantum computing company Alice & Bob said on Thursday that a quantum computer built from about 30,000 of its cat qubits could crack a Bitcoin private key in roughly an hour. The estimate comes from a preprint the company posted to the IACR Cryptology ePrint Archive, which targets secp256k1, the elliptic curve behind Bitcoin signatures, and puts the attack at no more than 29,588 physical qubits and 61.8 minutes. The paper treats those numbers as a ceiling because the Bitcoin calculation reuses circuits compiled to break RSA-2048 encryption. Superconducting Design Cat qubits are Alice & Bob’s own superconducting design. They suppress bit-flip errors in hardware, so error correction only has to catch phase-flips. That cuts the number of physical qubits behind each error-corrected logical qubit. In 2023, the company’s researchers put a 256-bit elliptic curve logarithm at 126,133 cat qubits and nine hours. In a whitepaper published on March 30, Google Quantum AI separated two kinds of attack. On-spend attacks hit a transaction before ...