Realizing low-loss, compact microwave-frequency resonators with spiral inductors

Low-loss microwave-frequency resonators play a vital role in quantum technologies, for example to implement bosonic qubits. While losses in coplanar waveguide resonators and three-dimensional cavities have been studied extensively [1, 2], compact resonator designs using spiral [3] or meandering [4] inductors remain less explored. Spiral resonators offer a smaller footprint and achieve higher effective inductances compared to coplanar waveguide resonators. Here, we study both spiral and coplanar waveguide resonators fabricated from wet-etched aluminum thin films. In preliminary experiments, we find quality factors in the single-photon regime exceeding 2 million for the spiral resonators. By investigating surface treatments such as ozone cleaning and optimizing the geometry, we expect to achieve even higher quality factors in the future.

[1] Chayanun, Lert, et al. APL Quantum 1.2 (2024)

[2] Kudra, M., et al. Applied Physics Letters 117.7 (2020)

[3] Tominaga, Y, et al. EPJ Quantum Technology 12.1 (2025)

[4] Chen, Qi-Ming, et al. Physical Review Research 5.4 (2023)