# The influence of pump coherence on the generation of position-momentum entanglement in down-conversion

## TL;DR

This paper investigates how the coherence of the pump laser influences the generation of position-momentum entanglement in photon pairs produced by nonlinear down-conversion, revealing that increased coherence enhances entanglement.

## Contribution

It provides both theoretical and experimental insights into how pump coherence affects position-momentum correlations and entanglement in photon pairs.

## Key findings

- Incoherent pump produces only position correlations.
- Higher pump coherence leads to momentum correlations.
- Enhanced coherence can generate entanglement.

## Abstract

Strong correlations in two conjugate variables are the signature of quantum entanglement and have played a key role in the development of modern physics. Entangled photons have become a standard tool in quantum information and foundations. An impressive example is position-momentum entanglement of photon pairs, explained heuristically through the correlations implied by a common birth zone and momentum conservation. However, these arguments entirely neglect the importance of the `quantumness', i.e. coherence, of the driving force behind the generation mechanism. We study theoretically and experimentally how the correlations depend on the coherence of the pump of nonlinear down-conversion. In the extreme case - a truly incoherent pump - only position correlations exist. By increasing the pump's coherence, correlations in momenta emerge until their strength is sufficient to produce entanglement. Our results shed light on entanglement generation and can be applied to adjust the entanglement for quantum information applications.