Dynamics of superconducting qubit coherence times due to fluctuations of two-level systems.*

Recent studies have shown that the stability of coherence times is strongly affected by two-level systems (TLSs). This is caused by chaotic frequency fluctuations of TLSs, which, when in proximity to the qubit resonance, significantly reduce its T₁ times. Understanding and mitigating this behavior is crucial to realize functional quantum processing devices based on superconducting qubits. In this work, we perform a long-time stability analysis of the qubit T₁ times as a function of qubit frequency utilizing the AC-Stark shifting technique [Carroll et al., arXiv:2105.15201]. We present an extensive analysis of the TLS distributions and their impact on T₁ times for different qubit sample materials and RF line configurations. Furthermore, our results provide insight into the effect of the noise spectrum on the behavior and density of TLSs.