Exact Stochastic Unraveling of an Optical Coherence Dynamics by Cumulant Expansion

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.Comment: 11 pages, 6 figure

Application of compressed sensing to the simulation of atomic systems

Compressed sensing is a method that allows a significant reduction in the number of samples required for accurate measurements in many applications in experimental sciences and engineering. In this work, we show that compressed sensing can also be used to speed up numerical simulations. We apply compressed sensing to extract information from the real-time simulation of atomic and molecular systems, including electronic and nuclear dynamics. We find that for the calculation of vibrational and optical spectra the total propagation time, and hence the computational cost, can be reduced by approximately a factor of five.Comment: 7 pages, 5 figure

Optical properties of a nanoegg–nanorod heterodimer : a quasi-static analysis

Plasmon coupling between the dipolar localized surface plasmons of a nanoegg and the longitudinal dipolar localized surface plasmons of a nearby gold nanorod is investigated within a dipolar-quasistatic limit. This was achieved by varying the core-offset of the nanoegg for different nanorod sizes at a fixed coupling distance. With respect to the plasmon peaks of the isolated nanoegg, we studied blue shifted, resonant, and red shifted nanorods. We show that besides plasmon-induced resonance shifts, which occurred in all three cases studied, transparency dips are induced in both the absorption and scattering spectra of the nanoegg–nanorod dimer. The latter effect depends on the plasmon detuning frequency and the nanorod absorption cross section. In comparison to a nanoegg–nanosphere dimer, the optical properties of the nanoegg–nanorod dimer are more enhanced.The National Research Foundation (NRF), the Czech Science Foundation and the University of Pretoria.https://www.osapublishing.org/josab/home.cfmhj2021Physic