Q-Factor Characterization of Superconducting Microwave Resonators

Microwave frequency domain resonators play an essential role in signal processing, qubit state manipulation, and readout in quantum technological applications. We present fabrication and characterization techniques for creating superconducting quarter-wavelength aluminum microwave resonators for use in circuit quantum electrodynamics (cQED). These resonators employ a coplanar waveguide geometry and are fabricated using photolithography. S-parameter analysis is then performed using a dilution fridge, providing a resonator quality factor (Q-factor) for use in characterization, primarily as a function of the capacitive coupling of the resonator body to the transmission line. We explored optimal capacitor lengths in order to maximize resonator response/Q-factor while minimizing potential noise due to over coupling, as well as strategies for minimizing crosstalk between resonators across a shared transmission line for use in composite quantum devices. The photolithography process and resonator fabrication recipe are also examined in order to maximize aggregate Q-factors whilst minimizing both fabrication time and Q-factor variability due to imperfections in the process.