Light-matter interactions in the vacuum of ultra-strongly coupled systems

TL;DR

This paper explores how the vacuum state in ultra-strong light-matter coupling regimes influences fundamental interaction processes, revealing that emitters interact with polariton modes rather than bare photons, with implications for various material systems.

Contribution

It introduces a theoretical framework showing that in ultra-strong coupling, the vacuum state alters the effective light-matter interaction, affecting how emitters couple to polariton modes instead of bare photons.

Findings

Effective coupling depends on vacuum state properties

Emitters interact with polariton modes, not bare photons

Framework applies broadly to different material systems

Abstract

We theoretically study how the peculiar properties of the vacuum state of an ultra-strongly coupled system can affect basic light-matter interaction processes. In this unconventional electromagnetic environment, an additional emitter no longer couples to the bare cavity photons, but rather to the polariton modes emerging from the ultra-strong coupling. As such, the effective light-matter interaction strength is sensitive to the properties of the distorted vacuum state. Different interpretations of our predictions in terms of modified quantum fluctuations in the vacuum state and of radiative reaction in classical electromagnetism are critically discussed. Whereas our discussion is focused on the experimentally most relevant case of intersubband polaritons in semiconductor devices, our framework is fully general and applies to generic material systems.