Dynamics and spectra of open quantum systems coupled to anharmonic environments

Kian Damezin; Brendon W. Lovett; Erik M. Gauger; Adam Burgess

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arXiv · 2608.27163

Dynamics and spectra of open quantum systems coupled to anharmonic environments

Kian Damezin·Brendon W. Lovett·Erik M. Gauger·Adam Burgess

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Abstract

In open quantum systems, the environment is typically modelled as a collection of harmonic oscillators, whereas realistic environments often exhibit unique non-Markovian effects due to the anharmonicity of the environment. Here we present a framework for modelling anharmonic environments in open quantum systems numerically exactly, in which, via a matching criterion, we map the anharmonic environment onto an effective harmonic one. This results in an effective spectral density that is a collection of shifted bare spectra arising from the non-equidistant energy gaps of the anharmonic environment, along with a unique zero-frequency term that effectively acts as static disorder on the system. This is due to the non-zero variance of the diagonal of the bath coupling operator. In tandem, we develop a framework for investigating the effects of environments comprising a few damped anharmonic modes where the matching criterion fails to work due to the non-Gaussianity of the environment. For both continuous and discrete damped anharmonic environments, this work investigates their unique influence on the system's dynamics, including enhanced non-Markovianity compared to a harmonic approximation, novel effects in the absorption spectrum, and the potential for anharmonic environments to enhance energy transport.

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Kian Damezin, Brendon W. Lovett, Erik M. Gauger, Adam Burgess. 2026-08-27. Dynamics and spectra of open quantum systems coupled to anharmonic environments. https://arxiv.org/abs/2608.27163

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