Hardware & Errors
Gate Fidelity
A measure of how accurately a quantum gate performs its intended operation, expressed as a percentage close to 100%.
Definition
Gate fidelity quantifies how closely a real, physically implemented quantum gate matches its theoretically perfect operation. A fidelity of 99.9% means the gate introduces an error roughly 0.1% of the time it's used — a critical metric since errors compound across the many gates in a real circuit.
Technical Definition
Fidelity is typically measured using randomized benchmarking, which applies long sequences of random gates and measures how the output distribution decays from the ideal expected result, isolating gate error from state preparation and measurement error.
Visual Explanation: An Analogy
Think of gate fidelity like the accuracy of a skilled craftsperson repeating the same precise cut thousands of times — even a tiny, consistent imprecision adds up to a noticeably flawed result after enough repetitions.
Real-World Use Cases
- The primary metric used to compare hardware quality across different quantum processors
- Determines how many gates can be chained together before a circuit becomes unreliable
- Directly determines the physical-to-logical qubit overhead needed for error correction