Two Level System Loss in Superconducting Microwave Resonators
David P. Pappas, Michael R. Vissers, David S. Wisbey, Jeffrey S. Kline, Jiansong Gao
High quality factor, i.e. low loss, resonators are important for quantum information storage and addressing. In this work we study the resonance frequency and loss in superconducting coplanar waveguide resonators as a function of temperature and power. We find that there is increased loss at low power and low temperature. The increased loss is attributed to the existence of two-level systems at the surfaces, interfaces, and in the bulk of insulators deposited on the structures. We show how the power dependence of the quality factor and the temperature dependence of the resonant frequency can both be used to find the zero temperature contribution to the loss from TLS. We find a close correspondence of these two independent measurements of TLS loss is evaluated. The most important aspect of these measurements is that the TLS contribution can be obtained from the frequency shift vs. temperature at high power, allowing for a reliable and fast measurement of the TLS contribution.