What is a quantum computer, and what is a qubit?
A computer that uses quantum physics to solve some problems far faster than ordinary ones. Its working parts are called qubits.
Ordinary bits are 0 or 1. Qubits can hold a mix of both, which lets some calculations, including the one behind Bitcoin's keys, be done in a radically different way.
Practical machines have limits in qubit count and error rates. In March 2026, Google estimated that breaking a Bitcoin-style key would take fewer than 500,000 physical qubits. That was an estimate of future requirements, not a demonstration.