Quantum error correction experiments on a 17-qubit superconducting processor. Part III: Defect correlation analysis and decoder calibration.*

The goal of decoding is to preserve the logical qubit state by inferring physical errors through processing of the error syndrome of stabilizer measurements. In this final part, we characterize both conventional qubit errors as well as non-conventional errors, such as leakage and crosstalk, using correlations between observed syndrome defects. We then calibrate minimum-weight perfect matching decoders with different sets of weights in order to minimize the logical error rate, and compare to those achieved using simple decoding strategies such as look-up tables and final majority voting.