2-Qubit Gate Fidelity
2-qubit gate fidelity is the standard accuracy metric for quantum computers, measuring the probability of a correct result after a computation passes through two quantum logic gates. A fidelity of 99.9% means ~1 error per 1,000 operations.
In quantum computing, even small fidelity differences are significant because errors compound across many gates:
- 99.99% (ionq): ~1 error per 10,000 operations — industry leading as of October 2025
- 99.9% (rigetti-computing, prototype): ~1 error per 1,000 — recent record, but only on small R&D system
- 99% (rigetti-computing, 108-qubit production system): ~1 error per 100 — signals scaling challenges
The gap between 99.9% and 99.99% is described as “huge” in practical quantum computing contexts (drury-2026-rigetti-2-qubit-fidelity).
High fidelity is a prerequisite for fault-tolerant quantum computing — without it, error correction makes things worse, not better.
See qubit, quantum-error-correction, quantum-computing.