  Qubit readout is a critical part of any quantum computer including the
superconducting-qubit-based one. The readout fidelity is affected by the
readout pulse width, readout pulse energy, resonator design, qubit design,
qubit-resonator coupling, and the noise generated along the readout path. It is
thus important to model and predict the fidelity based on various design
parameters along the readout path. In this work, a simulation methodology for
superconducting qubit readout fidelity is proposed and implemented using Matlab
and Ansys HFSS to allow the co-optimization in the readout path. As an example,
parameters are taken from an actual superconducting-qubit-based quantum
computer and the simulation is calibrated to one experimental point. It is then
used to predict the readout error of the system as a function of readout pulse
width and power and the results match the experiment well. It is found that the
system can still maintain high fidelity even if the input power is reduced by
7dB or if the readout pulse width is 40% narrower. This can be used to guide
the design and optimization of a superconducting qubit readout system.
