Influence of pump coherence on the quantum properties of spontaneous parametric down-conversion

TL;DR

This paper investigates how the coherence of the pump beam influences the entanglement properties of photon pairs generated via spontaneous parametric down-conversion, revealing that high pump coherence is essential for certain entanglement features.

Contribution

It provides a theoretical analysis showing the critical role of pump coherence in achieving continuous-variable entanglement in SPDC.

Findings

High pump coherence enables entanglement of transverse positions and momenta.

Signal and idler photon positions are correlated regardless of pump coherence.

Momentum correlations are absent even with momentum conservation.

Abstract

The correlation properties of the pump field in spontaneous parametric down-conversion are crucial in determining the degree of entanglement of generated signal and idler photons. We find theoretically that continuous-variable entanglement of the transverse positions and momenta of these photons can be achieved only if the coherence of the pump beam is sufficiently high. The positions of signal and idler photons are found to be correlated, even for an incoherent pump. However, the momenta of the signal and idler photons are not anti-correlated, even though transverse momentum is conserved.