TY - JOUR A1 - Palm, Timo A1 - Nalbach, Peter T1 - Nonperturbative environmental influence on dephasing T2 - Physical Review A N2 - Environmental noise leads to dephasing and relaxation in a quantum system. Often, a rigorous treatment of multiple noise sources within a system-bath approach is not possible. We discuss the influence of environmental fluctuations on a quantum system whose dynamics is dephasing already due to a phenomenologically treated additional noise source. For this situation, we develop a path-integral approach, which allows us to treat the system-environment coupling in a numerically exact way, and additionally we extend standard perturbative approaches. We observe strong deviations between the numerically exact and the perturbative results even for weak system-bath coupling. This shows that standard perturbative approaches fail for additional, even weak, system-bath couplings if the system dynamics is already dissipative. Y1 - 2017 UR - https://whge.opus.hbz-nrw.de/frontdoor/index/index/docId/2356 SN - 2469-9926 VL - 96 IS - 3 SP - 032105 ER -