Theory versus experiment for vacuum Rabi oscillations in lossy cavities (II): Direct test of uniqueness of vacuum

TL;DR

This paper investigates how different theoretical models of vacuum states in cavity QED affect vacuum Rabi oscillations, proposing that experimental data can distinguish between unique and non-unique vacuum theories.

Contribution

It introduces a reducible harmonic oscillator representation to model electromagnetic fields, predicting observable effects on Rabi oscillations that differ from traditional irreducible models.

Findings

Experimental data are consistent with a finite parameter $\

Collapse and revival phenomena depend on the parameter $\

Abstract

The paper continues the analysis of vacuum Rabi oscillations we started in Part I [Phys. Rev. A {\bf 79}, 033836 (2009)]. Here we concentrate on experimental consequences for cavity QED of two different classes of representations of harmonic oscillator Lie algebras. The zero-temperature master equation, derived in Part I for irreducible representations of the algebra, is reformulated in a reducible representation that models electromagnetic fields by a gas of harmonic oscillator wave packets. The representation is known to introduce automatic regularizations that in irreducible representations would have to be justified by ad hoc arguments. Predictions based on this representation are characterized in thermodynamic limit by a single parameter $\varsigma$, responsible for collapses and revivals of Rabi oscillations in exact vacuum. Collapses and revivals disappear in the limit $\varsigma\to\infty$. Observation of a finite $\varsigma$ would mean that cavity quantum fields are described by a non-Wightmanian theory, where vacuum states are zero-temperature Bose-Einstein condensates of a finite-particle bosonic oscillator gas and, thus, are non-unique. The data collected in the experiment of Brune {\it et al.} [Phys. Rev. Lett. {\bf{76}}, 1800 (1996)] are consistent with any $\varsigma>400$.