Detector Tomography on IBM Quantum Computers and Mitigation of Imperfect Measurement*

We use quantum detector tomography to characterize the qubit readout in terms of measurement POVMs on IBM Quantum Computers IBM Q 5 Tenerife and IBM Q 5 Yorktown. Our results suggest that the characterized detector model deviates noticeably from the ideal projectors. Further improvement on this characterization can be made by adopting two- or more-qubit detector models instead of independent single-qubit detectors for all the qubits in one device. We also find evidence indicating correlations in the detector behavior, i.e. the detector characterization is slightly altered when other qubits and their detectors are in operation. We also discuss how the characterized detectors' POVM can be used to estimate the ideal detection distribution.