Exact dynamics of non-additive environments in non-Markovian open quantum systems

TL;DR

This paper introduces a numerically-exact method based on TEMPO to accurately simulate non-additive, non-Markovian quantum system dynamics involving multiple baths, revealing complex phenomena like population inversion and the quantum Zeno effect.

Contribution

The paper develops a new efficient TEMPO-based technique for exact multi-bath quantum dynamics, surpassing previous approximations and uncovering novel effects.

Findings

Validated the method against approximate techniques.

Discovered a regime with quantum Zeno effect causing a fully mixed state.

Demonstrated the breakdown of approximate methods in strong coupling regimes.

Abstract

When a quantum system couples strongly to multiple baths then it is generally no longer possible to describe the resulting system dynamics by simply adding the individual effects of each bath. However, capturing such multi-bath system dynamics has up to now required approximations that can obscure some of the non-additive effects. Here we present a numerically-exact and efficient technique for tackling this problem that builds on the time-evolving matrix product operator (TEMPO) representation. We test the method by applying it to a simple model system that exhibits non-additive behaviour: a two-level dipole coupled to both a vibrational and an optical bath. Although not directly coupled, there is an effective interaction between the baths mediated by the system that can lead to population inversion in the matter system when the vibrational coupling is strong. We benchmark and validate multi-bath TEMPO against two approximate methods - one based on a polaron transformation, the other on an identification of a reaction coordinate - before exploring the regime of simultaneously strong vibrational and optical coupling where the approximate techniques break down. Here we uncover a new regime where the quantum Zeno effect leads to a fully mixed state of the electronic system.