Photo-induced dynamics with continuous and discrete quantum baths

TL;DR

This paper introduces a hybrid-bath method for simulating ultrafast quantum dynamics in complex molecules, effectively capturing continuous and discrete environmental effects with improved computational efficiency.

Contribution

A novel pure-state unraveled hybrid-bath approach that models continuous environments with discrete bosonic modes, overcoming limitations of previous methods in quantum chemistry and biology.

Findings

Accurately describes excitonic dynamics with fewer bosonic modes.

Achieves nearly tenfold computational speed-up.

Demonstrates significant environmental memory effects on dynamics.

Abstract

The ultrafast quantum dynamics of photophysical processes in complex molecules is an extremely challenging computational problem with a wide variety of fascinating applications in quantum chemistry and biology. Inspired by recent developments in open quantum systems, we introduce a pure-state unraveled hybrid-bath method that describes a continuous environment via a set of discrete, effective bosonic degrees of freedom using a Markovian embedding. Our method is capable of describing both, a continuous spectral density and sharp peaks embedded into it. Thereby, we overcome the limitations of previous methods, which either capture long-time memory effects using the unitary dynamics of a set of discrete vibrational modes or use memoryless Markovian environments employing a Lindblad or Redfield master equation. We benchmark our method against two paradigmatic problems from quantum chemistry and biology. We demonstrate that compared to unitary descriptions, a significantly smaller number of bosonic modes suffices to describe the excitonic dynamics accurately, yielding a computational speed-up of nearly an order of magnitude. Furthermore, we take into account explicitly the effect of a $\delta$-peak in the spectral density of a light-harvesting complex, demonstrating the strong impact of the long-time memory of the environment on the dynamics.