QED-based Optical Bloch Equations without electric dipole approximation: A model for a two-level atom interacting with a monochromatic X-ray laser beam

TL;DR

This paper derives new optical Bloch equations from bound-state QED without relying on the electric dipole approximation, enabling accurate modeling of two-level atoms interacting with X-ray lasers.

Contribution

It introduces a novel set of optical Bloch equations derived directly from bound-state QED, applicable to X-ray interactions where EDA fails.

Findings

Equations accurately describe atom-X-ray interactions.

Applicable to spectroscopy and Rabi oscillations in X-ray regimes.

Extends the theoretical framework beyond traditional EDA-based models.

Abstract

We derive a set of optical Bloch equations (OBEs) directly from the minimal-coupling Hamiltonian density of the bound-state quantum electrodynamics (bound-state QED). Such optical Bloch equations are beyond the former widely-used ones due to that there is no electric dipole approximation (EDA) on the minimal-coupling Hamiltonian density of the bound-state QED. Then our optical Bloch equations can describe a two-level atom interacting with a monochromatic light of arbitrary wavelength, which are suitable to study the spectroscopy and the Rabi oscillations of two-level atoms in X-ray laser beams since that the wavelength of X-ray is close to an atom to make the electric dipole approximation (EDA) invalid.