An Almost Analytical Approach to Simulating 2D Electronic Spectra

TL;DR

This paper presents an almost analytical method for simulating 2D electronic spectra, combining a unitary transformation with an improved population relaxation calculation to enhance accuracy and mechanistic understanding.

Contribution

It extends an analytic cumulant expansion approach to accurately include population relaxation effects in 2D spectra simulation, surpassing standard quantum master equations.

Findings

Accurately computes photon echo spectra of a two-level system.

Provides mechanistic insights into decoherence and relaxation processes.

Demonstrates high accuracy of the method through numerical simulations.

Abstract

We introduce an almost analytical method to simulate 2D electronic spectra as a double Fourier transform of the the non-linear response function (NRF) corresponding to a particular optical pulse sequence. We employ a unitary transformation to represent the total system Hamiltonian in a stationary basis that allows us to separate contributions from decoherence and phonon-mediated population relaxation to the NRF. Previously, one of us demonstrated the use of an analytic, cumulant expansion approach to calculate the decoherence term. Here, we extend this idea to obtain an accurate expression for the population relaxation term, a significant improvement over standard quantum master equation-based approximations. We numerically demonstrate the accuracy of our method by computing the photon echo spectrum of a two-level system coupled to a thermal bath, and we highlight the mechanistic insights obtained from our simulation.