Lorentz-Lorenz shift in a Bose-Einstein condensate

TL;DR

This paper analyzes the Lorentz-Lorenz shift in a Bose-Einstein condensate, demonstrating that contact interactions can be neglected due to atomic level shifts, leading to the classic local-field correction.

Contribution

It provides a quantum field theoretical derivation of the Lorentz-Lorenz shift in quantum degenerate gases, clarifying the role of contact interactions and atomic level shifts.

Findings

Contact interactions are negligible due to atomic level shifts.

The Lorentz-Lorenz local-field shift is derived from first principles.

The results clarify light-matter interactions in Bose-Einstein condensates.

Abstract

We study the quantum field theory of light-matter interactions for quantum degenerate atomic gases at low light intensity. We argue that the contact interactions between atoms emerging in the dipole gauge may be ignored. Specifically, they are canceled by concurrent infinite level shifts of the atoms. Our development yields the classic Lorentz-Lorenz local-field shift of the atomic resonance.