Polarisation and Transparency of Relativistically Rotating Two-Level Atoms

TL;DR

This paper investigates how relativistic rotation influences light-matter interactions in a gas of two-level atoms, revealing effects like depolarization and population inversion driven by acceleration and relativistic effects.

Contribution

It introduces a relativistic model incorporating acceleration-dependent rates and the Unruh effect to analyze light-matter interactions in rotating systems.

Findings

Relativistic rotation modifies atomic polarization and inversion.

Acceleration-induced effects can depolarize or invert atomic populations.

The approach uses local inertial frames to understand non-inertial motion effects.

Abstract

Electromagnetism and light-matter interaction in rotating systems is a rich area of ongoing research. We study the interaction of light with a gas of non-interacting two-level atoms confined to a rotating disk. We numerically solve the optical Bloch equations to investigate the how relativistic rotation affects the atoms' polarisation and inversion. The results are used to predict the steady-state stimulated emission seen by an observer at rest with the optical source in the laboratory frame. Competing physical effects due to time dilation and motion-induced detuning strongly modify solutions to the Bloch equations when the gas's velocity becomes relativistic. We account for the non-inertial motion by including acceleration-dependent excitation and emission rates, arising from a generalised Unruh effect. The effective thermal vacuum resulting from large accelerations de-polarises the gas while driving it towards population inversion, negating coherent driving due to the external light source. The results illustrate the intuitive, special-relativistic approach of assigning instantaneously comoving frames to understand non-inertial motion's influence when only local fields are physically significant.