Towards suppressing control-line crosstalk in superconducting quantum processors

Abstract

Microwave crosstalk poses a critical challenge to the scalability and fidelity of operations in superconducting quantum processors, especially in architectures with dense control wiring and small inter-qubit detuning. This thesis investigates the suppression of microwave crosstalk in a two-qubit system based on floating transmon qubits coupled both directly and via a tunable coupler. A theoretical model is developed by reducing the full capacitive network to analytically solvable circuits using Wye–Delta transformations and Kirchhoff’s laws. Symbolic expressions for qubit voltages are derived and interpreted as proxies for Rabi amplitudes, allowing crosstalk to be quantified in the frequency domain. Simulation results reveal that the interference between multiple coupling channels can be tuned to yield suppression in drive selectivity, controlled by parameters such as inter-qubit capacitance as well as coupler and qubit frequencies. Experimental cross-Rabi measurements validate the predicted suppression behavior, with selectivity reaching below −60 dB. While the analytical model captures the qualitative trends, quantitative discrepancies highlight the limitations of linear circuit approximations and motivate future work on quantum-level modeling. These results offer a framework for mitigating control-line crosstalk and advancing high-fidelity gate operations in superconducting devices.