Can we observe non-perturbative vacuum shifts in cavity QED?

TL;DR

This paper investigates whether strong confinement and high-impedance modes in cavity QED can lead to non-perturbative vacuum effects on a dipole's ground state, highlighting the potential for experimental realization.

Contribution

It provides analytic expressions for ground state energy shifts considering the full electromagnetic spectrum and identifies high-impedance modes as key to non-perturbative effects.

Findings

Confinement alone does not produce significant vacuum-induced corrections.

High-impedance modes like plasmons can enhance vacuum effects.

Non-perturbative regimes are theoretically accessible with engineered setups.

Abstract

We address the fundamental question whether or not it is possible to achieve conditions under which the coupling of a single dipole to a strongly confined electromagnetic vacuum can result in non-perturbative corrections to the dipole's ground state. To do so we consider two simplified, but otherwise rather generic cavity QED setups, which allow us to derive analytic expressions for the total ground state energy and to distinguish explicitly between purely electrostatic and genuine vacuum-induced contributions. Importantly, this derivation takes the full electromagnetic spectrum into account while avoiding any ambiguities arising from an ad-hoc mode truncation. Our findings show that while the effect of confinement per se is not enough to result in substantial vacuum-induced corrections, the presence of high-impedance modes, such as plasmons or engineered LC resonances, can drastically increase these effects. Therefore, we conclude that with appropriately designed experiments it is at least in principle possible to access a regime where light-matter interactions become non-perturbative.