Design and Characterization of Superconducting Aluminum Spiral Resonators towards Planar Bosonic Qubits

Bosonic qubits have emerged as a promising method for performing quantum computation on superconducting qubits. Typically, they are realized by coupling a high Q 3D cavity (Q_i>10⁷ to 10⁸) to a transmon qubit, which is then coupled to a low Q readout resonator (Q~10⁴)  [1, 2]. However, 3D cavities have a larger footprint compared to planar on-chip resonators, which can pose a challenge when scaling up bosonic qubit architectures. The most popular planar resonator is the coplanar waveguide (Q_i>10⁶), which tends to have lower Q-factor compared to 3D cavities. However, an effort was made to explore a geometric optimization to increase the internal quality factor, comparing Archimedian spiral resonators (ASRs) to coplanar waveguides using TiN as the superconductor [3]. Here, we discuss the prospects of using aluminum ASRs in planar bosonic qubit architectures as the storage resonator. 

[1] M. Reagor et al., Appl. Phys. Lett. 102, 192604 (2013)

[2] A. Joshi, K. Noh, Y. Y. Gao, Quantum Sci. Technol. 6 033001 (2021)

[3] Y. Tominaga et al., EPJ Quantum Technol. 12, 60 (2025).