Noise and signal distortions in qubit wiring

In this talk we highlight recent measurements to accurately characterize cryogenic qubit control and readout lines at microwave frequencies. Through combined theoretical and experimental studies, we quantify the qubit-gate errors that arise due to signal distortions and present direct measurements of the S-parameters of qubit control line components in situ [1]. We also demonstrate a cryogenic variable temperature noise source [2] to determine noise temperature of readout lines that use three-wave mixing parametric amplifiers. In addition, temperature-calibrated added noise can be used as a diagnostic resource to quantify thermalization requirements for qubit wiring [3]. Taken together our results provide a methodology for extrapolating system-level performance metrics for the i/o of large-scale quantum computers based on individual wiring components. [1] S. Simbierowicz, V. Y. Monarkha, S. Singh, N. Messaoudi, P. Krantz, R. E. Lake, "Microwave calibration of qubit drive line components at millikelvin temperatures", Appl. Phys. Lett. 120, 054004 (2022); [2] S. Simbierowicz, V. Vesterinen, J. Milem, A. Lintunen, M. Oksanen, L. Roschier, L. Grönberg, J. Hassel, D. Gunnarsson, R. E. Lake, "Characterizing cryogenic amplifiers with a matched temperature-variable noise source", Rev. Sci. Instr. 92, 034708 (2021); [3] A. Vaaranta, M. Cattaneo, R. E. Lake “Dynamics of a dispersively coupled transmon qubit in the presence of a noise source embedded in the control line” Phys. Rev. A 106, 042605 (2022)