Qubit Readout
How a quantum computer reports its answer, by dispersive microwave shifts or atomic fluorescence. It carries its own error rate, often worse than the gates.
Readout is how a quantum computer reports its answer, and each platform has its own dialect. Superconducting chips use dispersive readout: bounce a microwave tone off a resonator and the qubit's state subtly shifts the reflection. Trapped ions and neutral atoms use fluorescence: shine a laser, and the atom either glows (one state) or stays dark (the other). A camera literally photographs the answer.
Readout has its own error rate, separate from gate errors, and it's often worse; a machine with 99.9% gates and 98% readout loses more to the final photograph than to the computation. State-preparation-and-measurement (SPAM) error is the spec to hunt for in vendor papers, usually in the supplementary material, rarely in the press release.