Optimizing Charge Sensing Bias Conditions in the Presence of Noise

A heuristic, capacitance model including temperature and noise is used to evaluate quantum dot charge transitions detected by single-electron transistor (SET) charge sensing, finding that the optimal sensing condition occurs at surprisingly large charge sensor bias. We model the device with a capacitance solver, calculate the charge stability diagram, incorporate broadening due to temperature and noise, and evaluate the signal-to-noise ratio (SNR) for spin qubit measurements at different SET sensor bias conditions. The predicted sensor performance can be used to feedback on the design parameters and adjust coupling capacitance, dot size, etc. The optimal conditions are found at surprisingly large sensor bias, rather than the smallest bias that gives rise to the narrowest noise broadening. In general, this analytical method can be used to optimize the device design and to guide the device measurements.