2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/22025Motivated by recent experiments with Josephson-junction circuits, we analyze the influence of various noise sources on the dynamics of two-level systems at optimal operation points where the linear coupling to low-frequency fluctuations is suppressed. We study the decoherence due to nonlinear (quadratic) coupling, focusing on the experimentally relevant 1/f and Ohmic noise power spectra. For 1/f noise strong higher-order effects influence the evolution.minor corrections and clarificationsMesoscale and Nanoscale PhysicsQuantum Physicstext