Tow-level system (TLS) loss in amorphous dielectric materials has been intensively studied at millikelvin temperatures
due to its impact on superconducting qubit devices and incoherent detectors. However, the significance of TLS loss in
superconducting transmission lines at liquid helium temperatures remains unclear. This study investigates TLS loss in
amorphous SiO2 at liquid helium temperatures (about 4 K) within a frequency range of 130-170 GHz, using niobium
microstrip and coplanar waveguide resonators. Our results demonstrate notable power and temperature dependence of
dielectric loss, with the dielectric loss and quasiparticle loss exchanging dominance at around 4 K. These findings are
consistent with TLS models and provide crucial insights for the design of superconducting devices operating at liquid
helium temperatures.
https://arxiv.org/pdf/2407.08157