Exact Stochastic Unraveling of an Optical Coherence Dynamics by Cumulant Expansion

TL;DR

This paper introduces a numerically exact Monte Carlo method using cumulant expansion to accurately simulate the dynamics of open quantum systems, particularly for optical coherence in molecular excitons, across various environmental conditions.

Contribution

It presents a novel Monte Carlo scheme that is formally exact for harmonic environments and applicable to arbitrary temperatures and coupling strengths, improving simulation accuracy for quantum dynamics.

Findings

Accurately models optical coherence evolution in molecular systems.

Provides a comparison with standard simulation methods showing improved results.

Applicable to a wide range of environmental conditions and system parameters.

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.