Two-level System Loss: significant not only at Millikelvin

TL;DR

This paper investigates two-level system (TLS) loss in amorphous SiO2 at liquid helium temperatures, revealing significant power and temperature dependence that impacts superconducting device design.

Contribution

It provides the first detailed analysis of TLS loss in amorphous SiO2 at 4 K, highlighting the interplay between dielectric and quasiparticle losses.

Findings

TLS loss exhibits notable power dependence.

Dielectric loss and quasiparticle loss exchange dominance at 4 K.

Results align with TLS theoretical models.

Abstract

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 $SiO_2$ 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.