# Cosmological Birefringence and the Geometric Phase of Photons

## TL;DR

This paper demonstrates that cosmological birefringence results from an adiabatic geometric phase in photons caused by axion interactions, and proposes an analogue system using bi-isotropic media for simulation.

## Contribution

It reveals the geometric phase origin of cosmological birefringence and establishes an analogue system for experimental simulation.

## Key findings

- Cosmological birefringence linked to geometric phase in photon states.
- Equivalence between axion electrodynamics and bi-isotropic media.
- Potential for laboratory simulation of cosmological effects.

## Abstract

Regarding axion electrodynamics in the background flat FRW universe, we show that cosmological birefringence arises from an adiabatic noncyclic geometric phase that appears in the quantum state of photons because of their interaction with the axion field. We also show that the axion electrodynamics is equivalent to standard electrodynamics in time-dependent bi-isotropic magnetoelectric Tellegen media, which serves as an analogue system that can simulate cosmological birefringence.