Beyond the Rabi model: light interactions with polar atomic systems in a cavity

TL;DR

This paper extends the fundamental Rabi model to include permanent atomic dipoles, analyzing how these affect emission intensities and revealing conditions under which their effects can dominate or be engineered.

Contribution

It introduces a generalized Rabi model incorporating permanent dipoles and compares their emission effects to traditional counter-rotating terms using perturbative analysis.

Findings

Permanent dipoles can produce stronger emission lines than counter-rotating terms in some regimes.

The emission strength from permanent dipoles can be enhanced in low-dimensional or engineered spectral density systems.

Counter-rotating terms generally dominate emission in typical scenarios.

Abstract

The Rabi Hamiltonian, describing the interaction between a two-level atomic system and a single cavity mode of the electromagnetic field, is one of the fundamental models in quantum optics. The model becomes exactly solvable by considering an atom without permanent dipole moments, whose excitation energy is quasi-resonant with the cavity photon energy, and by neglecting the non resonant (counter-rotating) terms. In this case, after including the decay of either the atom or the cavity mode to a continuum, one is able to derive the well-known phenomenology of quasi-resonant transitions, including the fluorescence triplets. In this work we consider the most general Rabi model, incorporating the effects of permanent atomic electric dipole moments, and, based on a perturbative analysis, we compare the intensities of emission lines induced by rotating terms, counter-rotating terms and parity-symmetry-breaking terms. The analysis reveals that the emission strength related to the existence of permanent dipoles may surpass the one due to the counter-rotating interaction terms, but is usually much weaker than the emission due to the main, resonant coupling. This ratio can be modified in systems with a reduced dimensionality or by engineering the energy spectral density of the continuum.