Erasing Photon-Number Correlations through Hong-Ou-Mandel Interference

TL;DR

This paper investigates how Hong-Ou-Mandel interference can erase photon-number correlations in parametric down-conversion sources, revealing the separability of the output in the photon number basis and its implications for characterizing squeezed light.

Contribution

It introduces a hybrid approach to describe the state and demonstrates photon-number correlation measures' effectiveness in characterizing squeezed light sources.

Findings

Output is separable in the photon number basis.

Photon-number correlation measures are useful for source characterization.

Interference can erase photon-number correlations in the system.

Abstract

A parametric down-conversion source interfering on a beam splitter can be described as both a source of entangled N00N-states or a source of independent, and thus uncorrelated squeezers. The disparity between these outcomes can be attributed to whether one takes a standard discrete- or continuous-variable approach to describing the system. More precisely, this difference in output is due to the types of measurements involved and the way in which the data is processed, as both setups are identical, clearly identical states are produced. Here we take a hybrid approach to describe the state, which is generated by parametric down-conversion as input state, and investigate the measurements of the output ports of the interferometer using photon number resolved detection. We show that the output of this interference is separable in the photon number picture and demonstrate the worth of photon-number correlation measures for the characterization of squeezed light sources for hybrid applications like Gaussian boson-sampling.