title: Exact stochastic unraveling of an optical coherence dynamics by cumulant expansion.
abstract: A numerically exact Monte Carlo scheme for calculation of open quantum system dynamics is proposed and implemented. The method consists of a Monte Carlo summation of a perturbation expansion in terms of trajectories in Liouville phase-space with respect to the coupling between the excited states of the molecule. The trajectories are weighted by a complex decoherence factor based on the second-order cumulant expansion of the environmental evolution. The method can be used with an arbitrary environment characterized by a general correlation function and arbitrary coupling strength. It is formally exact for harmonic environments, and it can be used with arbitrary temperature. Time evolution of an optically excited Frenkel exciton dimer representing a molecular exciton interacting with a charge transfer state is calculated by the proposed method. We calculate the evolution of the optical coherence elements of the density matrix and linear absorption spectrum, and compare them with the predictions of standard simulation methods.
authors.affiliation: Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-121 16 Prague 2, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Olšina
authors.affiliation: Mads Clausen Insitute, University of Southern Denmark, 6400 Sønderborg, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Kramer
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kreisbeck
authors.affiliation: Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, CZ-121 16 Prague 2, Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Mančal