Modeling open quantum systems -- quantum systems coupled to a bath -- is of\nvalue in condensed matter theory, cavity quantum electrodynamics, nanosciences\nand biophysics. The real-time simulation of open quantum systems was advanced\nsignificantly by the recent development of chain mapping techniques and the use\nof matrix product states that exploit the intrinsic entanglement structure in\nopen quantum systems. The computational cost of simulating open quantum\nsystems, however, remains high when the bath is ex…