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Noise and error
Measurement desk
Noise is unwanted change in a quantum state while a circuit runs. The measurement desk separates that physical disturbance from ordinary sampling error, and writes both down beside every device result.
Two different errors
Sampling error remains even on a perfect simulator. It is the wobble of a finite number of shots, described under measurement and sampling. Noise error is extra: a gate that was not in the list, a qubit that drifts while it waits, a readout that flips after the state was correct.
Depth from the quantum circuit model matters here. A deeper schedule gives a device more time to accumulate those extra processes. Width matters because more qubits mean more places for a readout to fail.
What the desk records
Each noisy study names the channel, the rates, and whether mitigation was applied. Mitigation is a correction to the samples. It is not a proof that the device followed the ideal gate list. An ideal state-vector simulation run stays in the note as the comparison, not as the device’s result.
When the classical optimiser and the device share a loop, noise changes the numbers the optimiser sees. That loop is hybrid execution. The desk does not move angles until the noise model on the shots is stated.
Finding from this desk
Ideal circuits and device circuits are different experiments. The desk’s finding is that an error model has to be named — depolarising, readout flips, or idle decoherence — before a gap between simulator and device is called a discovery.