Coupling function from bath density of states

TL;DR

This paper introduces a method to infer the coupling between a quantum system and its environment using the environment's density of states, enabling more accurate modeling of relaxation dynamics in materials.

Contribution

It presents a novel approach to derive system-environment coupling parameters directly from experimentally measurable density of states.

Findings

Confirmed Debye model's DOS as an Ohmic bath

Matched real phonon DOS to Lorentzian coupling functions

Determined material-specific coupling parameters for gold, YIG, and iron

Abstract

Modelling of an open quantum system requires knowledge of parameters that specify how it couples to its environment. However, beyond relaxation rates, realistic parameters for specific environments and materials are rarely known. Here we present a method of inferring the coupling between a generic system and its bosonic (e.g., phononic) environment from the experimentally measurable density of states (DOS). With it we confirm that the DOS of the well-known Debye model for three-dimensional solids is physically equivalent to choosing an Ohmic bath. We further match a real phonon DOS to a series of Lorentzian coupling functions, allowing us to determine coupling parameters for gold, yttrium iron garnet (YIG) and iron as examples. The results illustrate how to obtain material-specific dynamical properties, such as memory kernels. The proposed method opens the door to more accurate modelling of relaxation dynamics, for example for phonon-dominated spin damping in magnetic materials.