Evaluating NbTiN as a platform for 3D circuit QED

Disordered superconducting films with large superconducting gaps could be 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 [1, 2]. This allows us to extract the loss contributions from the material under investigation as well as the package and substrate. We have measured the loss contributions for Niobium Titanium Nitride (NbTiN), a superconductor offering the largest gap of the disordered nitrides, and find that it can be readily patterned into resonant structures with internal quality factors of several million. Furthermore, we have used this material as a base layer for transmon qubits with T1 lifetimes exceeding 100 μs. In addition to characterizing the dielectric losses that usually dominate the performance of superconducting circuits, we also consider the material losses that occur when the material is prepared in the thin-film regime.



References:

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

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