Optical nonlinearity of cold atomic ensemble driven by strong coherent field in a saturation regime

TL;DR

This paper analyzes the optical nonlinearity of cold atomic ensembles driven by strong coherent fields, showing how collective effects can enhance nonlinearity and impact quantum communication protocols.

Contribution

It provides a microscopic analysis of dielectric susceptibility in driven atomic ensembles, highlighting the potential for magnified optical nonlinearity through manipulation of pump and density.

Findings

Collective atomic responses can be interpolated from dilute to dense media.

Optical nonlinearity can be significantly enhanced by adjusting pump and density.

Limitations for quantum communication protocols using entangled photons are discussed.

Abstract

We present a microscopic analysis and evaluation of the dielectric susceptibility of a dielectric medium consisting of vector-type two-energy-level atoms responding on a weak probe mode when the atoms are driven by a strong coherent field. Each atom, in an environment of others, exists as a quasiparticle further structuring a bulk medium. In a limit of dilute atomic gas, the dynamics of each atom follows the Mollow-type nonlinear excitation regime, and the medium susceptibility collectivizes the individual atomic responses to the probe mode. We outline how the collective dynamics can be interpolated up to a dense medium, and we argue from general positions that in such a medium the optical nonlinearity and, in particular, its parametric part could be significantly magnified by manipulating both the coherent pump and the sample density. That indicates certain limitations for potential capabilities of quantum communication protocols utilizing the entangled photons, created by a parametric process, as a main resource of quantum correlations.