Quantum Gate Fidelity
A measure of how accurately a quantum operation (gate) is executed. Higher is better; errors accumulate rapidly, so fidelity is one of the most important metrics in quantum computing.
Quantum gate fidelity measures how accurately a quantum computer executes a specific quantum operation. A gate fidelity of 99% means the operation introduces a 1% error rate. A fidelity of 99.9% means a 0.1% error rate.
This matters enormously because quantum computations require many sequential gate operations. Errors accumulate: a 99% fidelity gate applied 100 times gives roughly a 37% chance of a correct final result. A 99.9% fidelity gate applied the same number of times gives roughly a 90% chance.
The threshold for fault-tolerant quantum computing, where error correction can keep pace with error introduction, is typically estimated to require two-qubit gate fidelities above 99%. Some analyses require 99.9% or higher.
Two-qubit gates (operations between two qubits simultaneously) are harder to execute accurately than single-qubit gates, and are usually the limiting factor.
Quantinuum in Broomfield holds the record for two-qubit gate fidelity, at 99.9%+. This is one of the key reasons Quantinuum is considered the most technically advanced commercial quantum computing company, even if it is less well known than IBM or Google.