The justification of 'Two-Level Approximation' in strong light-matter interaction

TL;DR

This paper examines the limitations of the Two-Level approximation in strong light-matter interactions, revealing that the third level significantly affects system dynamics and that the approximation is often invalid in this regime.

Contribution

It provides a detailed analysis of when the Two-Level model fails in strong coupling regimes and clarifies the conditions under which it can still be justified.

Findings

The third level greatly influences system evolution in strong coupling.

The Two-Level approximation is generally invalid in the strong coupling regime.

Conditions for the validity of the Two-Level model are identified.

Abstract

We investigate the influence of the additional third level on the dynamic evolution of a Two-Level system interacting with a coherent field in the strong coupling regime where Rotating Wave Approximation is not valid. We find that the additional level has great influence on the evolution of the system population. Our results show that the Two-Level model is not a good approximation in this strong light-matter coupling regime. We further investigate the parameter space where the Two-Level model can still be justified.