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  1. OCT

    30

    Wednesday

    CSI Q Seminar

    "Characterizing readout in quantum computers: does the reading '0' really mean 0 and '1' really 1?"

    Presented by Tzu-Chieh Wei, Stony Brook University

    3 pm, Training Room, Bldg 725

    Wednesday, October 30, 2019, 3:00 pm

    Hosted by: Layla Hormozi

    Typical quantum computation includes three stages: state initialization, gate operations and readout. There are tomographic tools on quantum state and process tomography, as well as one that is often ignored, i.e. the detector tomography. It is important to characterize the readout in interpreting experiments on quantum computers. We use quantum detector tomography to characterize the qubit readout in terms of measurement POVMs on IBM Quantum Computers (e.g. IBM Q 5 Tenerife and IBM Q 5 Yorktown). Our results suggest that the characterized detector model deviates from the ideal projectors, ranging from 10 to 40 percent. This is mostly dominated by classical errors, evident from the shrinkage of arrows in the corresponding Bloch-vector representations. There are also small deviations that are not `classical', of order 3 percent or less, represented by the tilt of the arrows from the z axis. 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 (to a few percent) when other qubits and their detectors are in operation. Such peculiar behavior is consistent with characterization from the more sophisticated approach of the gate set tomography. Finally, we also discuss how the characterized detectors' POVM, despite deviation from the ideal projectors, can be used to estimate the ideal detection distribution.

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