Gain-induced spectral non-degeneracy in type-II parametric down-conversion

TL;DR

This paper reveals a gain-induced spectral shift in type-II parametric down-conversion, showing a transition from degenerate to non-degenerate PDC at high gain, which impacts photon pair distinguishability, based on a rigorous theoretical model.

Contribution

It introduces and analyzes a novel gain-induced spectral non-degeneracy effect in type-II PDC, highlighting limitations of approximate models.

Findings

Spectral non-degeneracy increases with gain.

The effect is driven by second-order dispersion terms.

Approximate models fail to predict this effect.

Abstract

We demonstrate the novel effect of gain-induced spectral shifts in the type-II parametric down-conversion (PDC) process, which results in a transition from degenerate to non-degenerate PDC with increasing parametric gain. This effect, originating from the second-order dispersion terms, significantly alters the properties of PDC in the high-gain regime, where it leads to increased distinguishability of the generated photon pairs. The effect is established by evaluating a rigorous theoretical model, which is based on solving a system of coupled integro-differential equations for monochromatic operators. The widely used spatially-averaged approximate model fails to reproduce this important effect.