Error mitigation
Some common sources of error can be more systematically tackled since measuring the classical outcome of quantum hardware is not free of errors. Luckily, this type of error can be tackled by observing the common errors that are made upon readout and compensating for post-processing the outcome.
If we look into our IBM Quantum Experience service once more, we could request the readout error for a given device. In Figure 9.6, we can observe how any operation that’s done on qubits 10 and 15, upon measurement, could be misinterpreted:
Figure 9.6 – Readout error on IBM’s Toronto device (27 superconducting qubits Falcon r4)
These statistics can be derived by the simple act of placing an operation whose outcome is known (for example, X|ψ⟩) and recording the discrepancies upon measuring it for a significant number of tryouts. If those statistics are known, you can compensate for the measurements that are obtained...