Design and Modeling of Double-Fold Superconducting High-Q Coplanar Waveguide Resonators for Quantum Applications

In this article, we present a novel design of a compact, double-fold half-wave superconducting coplanar waveguide resonator, specifically optimized for quantum readout. The geometry offers advantages in terms of scalability and allows for a more compact integration of qubits per unit area. The superconducting resonators are designed to operate within a fundamental frequency range of 1.9–1.95 GHz, utilizing both gap and finger coupling schemes. The devices are fabricated using thin aluminum films deposited on high-resistivity sapphire substrates. The proposed resonators exhibit quality factor (Q$_{L}$) of $\text{2.9}\times \text{10}^{\text{5}}$ and $\text{1.58}\times \text{10}^{\text{3}}$ for gap coupled and finger coupled, respectively, during experimental measurements. The simulated Q$_{L}$ of single-folded meander line resonators are found to be $\text{4.65}\times \text{10}^{\text{5}}$ and 258.42, for gap coupled and finger coupled, respectively, and for comparison purpose at similar operating frequency. A comprehensive analysis of the microwave transmission spectra was conducted at cryogenic temperatures near 10 mK, across very high input drive powers ($-$30 to $-$10 dBm). Experimental results show a good agreement with simulations and the equivalent lumped circuit model. Notably, the proposed design reduces the physical footprint of the resonator devices up to 28.2$\%$ compared to conventional single-fold meandered structures. The resonators demonstrate strong potential for integrating qubits with readout and control buses in quantum information processing, which require a Q$_{L}$ between 10⁴–10⁵. They also being well-suited for cryogenic detector applications that utilize microwave kinetic inductance detector arrays in frequency multiplexing for different coupling schemes.