Spatiotemporal correlations in entangled photons generated by spontaneous parametric down conversion

TL;DR

This paper investigates how frequency information influences the spatial entanglement of photon pairs generated by SPDC, revealing correlations that affect the total entanglement and emphasizing the need to consider these effects in quantum optics experiments.

Contribution

It demonstrates the impact of frequency-space correlations on the purity and entanglement of photon pairs in SPDC, highlighting an often overlooked aspect in entanglement generation.

Findings

Frequency information affects the spatial purity of photon pairs.

Correlations between frequency and space degrees of freedom exist.

Total entanglement must account for frequency-space correlations.

Abstract

In most configurations aimed at generating entangled photons based on spontaneous parametric down conversion (SPDC), the generated pairs of photons are required to be entangled in only one degree of freedom. Any distinguishing information coming from the other degrees of freedom that characterize the photon should be suppressed to avoid correlations with the degree of freedom of interest. However, this suppression is not always possible. Here, we show how the frequency information available affects the purity of the two-photon state in space, revealing a correlation between the frequency and the space degrees of freedom. This correlation should be taken into account to calculate the total amount of entanglement between the photons.