Quantum Threat to Bitcoin: IonQ Estimates 20,000-Qubit Breakthrough

IonQ, an American company specializing in trapped-ion technology and listed on the NYSE, has put a precise number on the quantum threat to Bitcoin. According to their study, a fault-tolerant quantum computer with roughly 20,000 physical qubits could break the elliptic curve cryptography that secures Bitcoin signatures in just under a month.

The company estimates that such a machine would require 19,397 physical qubits, organized into 1,457 logical qubits, and would need to run for 25.7 straight days per attack attempt. The calculation also requires 39 million Toffoli logic gates. However, it's essential to note that these numbers don't guarantee the key; IonQ calculated a rigorous lower bound of 40.7% success per single attempt, rising to around 63.3% under more optimistic mathematical assumptions.

The security of Bitcoin's system rests on one fact: deriving the private key from the public one is computationally impossible today. Shor's algorithm on a sufficiently large machine flips that fact on its head. An address becomes vulnerable only once its public key ends up in the clear on the blockchain, which happens when an address broadcasts a transaction.

The good news is that post-quantum algorithms already standardized by NIST, such as ML-DSA and SLH-DSA, stay out of reach of this class of attack. For Bitcoin, the path forward is clear but not painless: it needs to migrate to quantum-resistant signatures. In a decentralized system, a change like that requires network consensus, a process that's slow by design.