# Quantum induced birefringence in nonlinear optical materials

## TL;DR

This paper explores how quantum fluctuations in nonlinear optical materials can induce birefringence, leading to polarization-dependent light speeds, with potential observable effects in squeezed vacuum states.

## Contribution

It introduces the concept of quantum fluctuation-induced birefringence in nonlinear dielectrics and analyzes its characteristics and potential observability.

## Key findings

- Quantum fluctuations can couple with nonlinearities to produce birefringence.
- In squeezed vacuum states, birefringence can have opposite sign to classical Kerr effect.
- Estimated effects suggest possible experimental detection.

## Abstract

The influence of quantum fluctuations of the electromagnetic field on the propagation of a polarized light wave in a nonlinear dielectric is investigated. It is shown that in some cases, the fluctuations couple to the optical nonlinearities of the medium and make its refractive index dependent on the polarization of the propagating wave. As a consequence, two light waves propagating in a same direction but with different polarizations will have different speeds, so there will be a Kerr-effect birefringence induced by quantum fluctuations. We consider the case of the electromagnetic field in a squeezed vacuum state, where there are regions where the mean squared electric field can be negative and the birefringence effect has the opposite sign to the Kerr effect in classical physics. We give some estimates for the magnitude of these effects, and discuss their possible observability.