Eliminating Spectral Distinguishability in Ultrafast Spontaneous Parametric Down-conversion

TL;DR

This paper experimentally demonstrates a spectral compensation scheme that eliminates spectral distinguishability in ultrafast spontaneous parametric down-conversion, significantly improving polarization entanglement quality without spectral filtering.

Contribution

The study validates and implements a spectral compensation method to enhance polarization entanglement in ultrafast SPDC, reducing spectral distinguishability effects.

Findings

Spectral distinguishability was eliminated in the experiment.

Achieved polarization visibility of 97.9% without spectral filtering.

Confirmed the effectiveness of the spectral compensation scheme.

Abstract

Generation of polarization-entangled photon pairs with a precise timing through down-conversion of femtosecond pulses is often faced with a degraded polarization entanglement quality. In a previous experiment we have shown that this degradation is induced by spectral distinguishability between the two decay paths, in accordance with theoretical predictions. Here, we present an experimental study of the spectral compensation scheme proposed and first implemented by Kim et al. in 2002. By measuring the joint spectral properties of the polarization correlations of the photon pairs, we show that the spectral distinguishability between the down-converted components is eliminated. This scheme results in a visibility of 97.9+/-0.5% in the polarization basis without any spectral filtering.