Frequency-dependent two-level system loss in tantalum superconducting resonators

Two-level system (TLS) loss currently limits lifetimes of superconducting microwave resonators and qubits. This TLS loss is typically considered to be frequency-independent at microwave frequencies and millikelvin temperatures. Measuring several resonances of multi-wavelength coplanar waveguide resonators [1], we empirically evaluate this assumption. Comparing tantalum films etched with fluorine and chlorine chemistries, we find that resonators etched with F ions feature low, frequency independent loss, while those etched with Cl ions show greater loss which increases from 4 GHz to 7 GHz. This work demonstrates the power of using multi-wavelength resonators for analyzing microwave loss.

[1] C. Chen et al., arXiv:2506.08130 (2025)