Master's Defense: Johann Bock Severin

Superconducting Qubit Readout in Theory, Experiment and Simulation

For superconducting qubits to be a viable platform for large-scale quantum information processing, a high-fidelity readout is required. This thesis investigates the underlying physics describing the system and time evolution in an initialization and readout sequence in order to study how different physical parameters contribute to the State Preparation and Measurements (SPAM) errors. By calibrating a single superconducting qubit, a simulation model is built using the stochastic master equation to simulate the dispersive approximation of a qubit-resonator system. The model is capable of producing realistic plots of IQ measurements that have similar distributions and SPAM fidelity as measured in the laboratory. The model is used to estimate the contribution to the infidelity from three factors: non-zero temperature, energy decay during measurement, and inefficient measurement. We conclude that non-zero temperature is the biggest contributor to the analyzed system. The model is further used to simulate the system with marginal improvements. This serves as a basis for discussing how to improve superconducting qubit readout.