Magic frequencies in atom-light interaction for precision probing of the density matrix

TL;DR

This paper investigates a specific 'magic frequency' in atom-light interactions where absorption becomes insensitive to atomic population distributions, enabling more robust hyperfine population measurements.

Contribution

The paper introduces the concept of a magic frequency in alkali vapor atoms, supported by theoretical analysis and experimental validation, for improved atomic state probing.

Findings

Identification of a magic frequency where absorption is population-independent

Experimental confirmation of the theoretical predictions

Potential for more accurate hyperfine population measurements

Abstract

We analyze theoretically and experimentally the existence of a {\it magic frequency} for which the absorption of a linearly polarized light beam by vapor alkali atoms is independent of the population distribution among the Zeeman sub-levels and the angle between the beam and a magnetic field. The phenomenon originates from a peculiar cancelation of the contributions of higher moments of the atomic density matrix, and is described using the Wigner-Eckart theorem and inherent properties of Clebsch-Gordan coefficients. One important application is the robust measurement of the hyperfine population.