System Noise Calibration for Qubit Readout

A key aspect in designing a high-fidelity readout chain for superconducting qubit systems is the ability to accurately characterize and calibrate the system noise added by various hardware components at different stages. The readout chain typically includes high insertion loss components such as circulators, filters, and directional couplers, positioned between the qubit device and the first-stage amplifier (e.g., TWPA or JPA), which lowers the net SNR. In order to optimize and improve the overall performance, it is crucial to precisely quantify these losses, as well as to accurately extract readout SNR at the qubit output and the noise added by the TWPA. Traditional methods for noise characterization often require complex hardware, multiple cooldown cycles, and provide limited accuracy in estimating the attenuation between the qubit and the amplifier. In this study, we demonstrate a streamlined experimental setup that extracts all the above-mentioned key parameters in a single cooldown.