Characterizing Midcircuit Measurements on a Superconducting Qubit Using Gate Set Tomography

Key applications of quantum computing, including error correction, rely critically on the capability to measure (read out) the state of selected quantum bits, without disturbing other qubits or terminating the computation. Such $m{{0}{0ex}}i{{0}{0ex}}d{{0}{0ex}}c{{0}{0ex}}i{{0}{0ex}}r{{0}{0ex}}c{{0}{0ex}}u{{0}{0ex}}i{{0}{0ex}}t$ $m{{0}{0ex}}e{{0}{0ex}}a{{0}{0ex}}s{{0}{0ex}}u{{0}{0ex}}r{{0}{0ex}}e{{0}{0ex}}m{{0}{0ex}}e{{0}{0ex}}n{{0}{0ex}}t{{0}{0ex}}s$ are now being implemented in a few cutting-edge platforms, but their development is hindered by lack of a means to measure their performance and characterize the errors that they produce. The authors show how to extend a popular tomography method for precise characterization of midcircuit measurements, and using their QILGST protocol discover a pernicious kind of non-Markovian error, which once identified can be handled.