  In this study, we employ purity benchmarking (PB) to explore the dynamics of
gate noise in a superconducting qubit system. Over 1110 hours of observations
on an Xmon qubit, we simultaneously measure the coherence noise budget across
two different operational frequencies. We find that incoherent errors, which
predominate in overall error rates, exhibit minimal frequency dependence,
suggesting they are primarily due to wide-band, diffusive incoherent error
sources. In contrast, coherent errors, although less prevalent, show
significant sensitivity to operational frequency variations and telegraphic
noise. We speculate that this sensitivity is due to interactions with a single
strongly coupled environmental defect -- modeled as a two-level system -- which
influences qubit control parameters and causes coherent calibration errors. Our
results also demonstrate that PB offers improved sensitivity, capturing
additional dynamics that conventional relaxation time measurements cannot
detect, thus presenting a more comprehensive method for capturing dynamic
interactions within quantum systems. The intricate nature of these coherence
dynamics underscores the need for further research.
