Non-Hermitian Hamiltonian Approach for Two-Dimensional Coherent Spectra of Driven Systems

TL;DR

This paper introduces a non-Hermitian Hamiltonian approach for simulating two-dimensional coherent spectra, offering a new analytical method that captures dominant pathways and relaxations more effectively than traditional response-function formalism.

Contribution

The study develops a quasi-Green function framework for the NHH method and demonstrates its effectiveness in modeling 2DCS in driven systems, surpassing the RF formalism in handling relaxation and control fields.

Findings

NHH method accurately reproduces experimental 2DCS signals.

NHH provides all dominant Liouville paths analytically.

NHH overestimates relaxation effects but captures key dynamics.

Abstract

Two-dimensional coherent spectroscopy (2DCS) offers significant advantages in terms of high temporal and frequency resolutions and signal-to-noise ratio. Until now, the response-function (RF) formalism has been the prevalent theoretical description. In this study, we compare the non-Hermitian Hamiltonian (NHH) method with the RF formalism in a three-level system with a constant control field. We obtain the signals from both approaches and compare their population dynamics and 2DCS. We propose the quasi-Green functions for the NHH method, which allows all dominant Liouville paths to be inferred. We further simulate the 2DCS of Rh(CO)$_2$C$_5$H$_7$O$_2$ (RDC) dissolved in hexane with the NHH method, which is in good agreement with the previous experiments. Although the NHH method overestimates relaxations, it provides all important paths by analytical solutions, which are different from the four paths used in the RF formalism. Our results demonstrate that the NHH method is more suitable than the RF formalism for investigating the systems including relaxation and control fields via the 2DCS.