Spin-boson dynamics: A unified approach from weak to strong coupling

TL;DR

This paper introduces a new approximation method for modeling the dynamics of a two-level quantum system interacting with a harmonic bath, effective across various temperatures and coupling strengths, aligning well with existing methods.

Contribution

It proposes a unified approximation scheme that captures intra-blip correlations exactly and includes inter-blip interactions to first order, covering a broad parameter regime.

Findings

Excellent agreement with perturbative approaches in proper regimes

Consistent with ab-initio path-integral results

Applicable across a wide range of temperatures and coupling strengths

Abstract

We present a novel approximation scheme to describe the influence of a harmonic bath on the dynamics of a two-level particle over almost the whole regime of temperatures and coupling to the environment, for a wide class of bath spectral densities. Starting from the exact path-integral solution for the two-level system density matrix, effective intra-blip correlations are fully included, while inter-blip and blip-sojourn interactions are considered up to first order. In the proper regimes, an excellent agreement with conventional perturbative approaches and ab-initio path-integral results is found.