Probing two-level systems with a surface acoustic wave resonator

Abstract

Parasitic two-level systems (TLSs) cause detrimental effects on the performance of superconducting quantum devices. To mitigate this problem, a better physical understanding of the TLS coupling mechanism is crucial. In this thesis, a new approach for probing TLSs using a surface acoustic wave (SAW) resonator is presented. Having a small mode spacing, the SAW resonator enables an investigation of the frequency noises caused by TLSs at many different frequencies simultaneously. We report a novel result of the correlated frequency noise caused by TLSs. The correlations of the noise diminish with increasing detuning, which is in agreement with the prediction of the TLS model. However, the frequency noises also show negative correlations, which cannot be explained by the current physical model. Additionally, the frequency noise correlation between different modes shows a power and temperature-dependent behavior. Although some previous experiments have reported the power and temperature dependence of the frequency noise spectra, the relationships of the noise at several different frequencies have not been studied. Therefore, further investigations, both experimental and theoretical aspects, of the multifrequency noise beyond this work are required.