Evaluating microwave loss associated with disordered superconductors

Disordered superconducting films are an attractive platform for realizing quantum devices. They offer an intrinsic nonlinearity due to their large kinetic inductance (KI) and have the potential to operate in magnetic fields and at higher temperatures. Evaluating the utility and limitations of a material requires understanding the microwave loss mechanisms associated with that material. We use a 3D ‘hanger'-style package to measure lithographically patterned multimode stripline resonators, allowing us to disentangle the loss contributions from different regions and predict device performance [1, 2]. We have measured the loss contributions for thick-film Niobium Titanium Nitride (NbTiN) and used our results to predict the performance of transmons with measured relaxation times exceeding 100 μs. Furthermore, we have extended these loss characterization techniques to determine the amount of conductor loss present in thin-film NbTiN, a regime of interest for realizing KI based devices. We find that the conductor loss scales with the KI fraction in a manner predicted by Mattis-Bardeen theory.

References:

[1] C. Axline, et al. Appl. Phys. Lett. 109, 042601 (2016).

[2] S. Ganjam, et al. Nat. Commun. 15, 3687 (2024).