QFit: simplifying calibration and parameter fitting for superconducting circuits

We present QFit, a Python-based application for extracting parameters of superconducting circuits from measured spectroscopy data. Through its streamlined graphical user interface, users interactively calibrate measurement data, extract data points, and perform parameter fitting. QFit supports modeling of a wide range of circuit quantum electrodynamic systems, leveraging the Python library scqubits as its backend simulator. The application also encompasses a suite of features to enhance the precision of parameter fitting, including: assisted flux crosstalk calibration, automatic identification of resonance peaks, and interactive fitting-by-eye prior to numerical fitting. The extracted parameters can be seamlessly passed on to scqubits, facilitating subsequent numerical simulations. QFit provides a convenient and efficient pipeline from experimental measurements to theoretical simulations, accelerating the process of developing novel superconducting circuit systems.