Full-mode Characterisation of Correlated Photon Pairs Generated in Spontaneous Downconversion

TL;DR

This paper comprehensively characterizes the full spatial mode correlations of photon pairs generated via spontaneous downconversion, including effects of structured pump beams, and performs full quantum tomography in a high-dimensional basis.

Contribution

It introduces a method to analyze full-mode correlations in Laguerre-Gauss basis and demonstrates quantum tomography of bi-photon states in a 16-dimensional space.

Findings

Full-mode correlation analysis in Laguerre-Gauss basis.

Impact of structured pump beams on spatial correlations.

Successful quantum tomography in high-dimensional space.

Abstract

Spontaneous parametric downconversion is the primary source to generate entangled photon pairs in quantum photonics laboratories. Depending on the experimental design, the generated photon pairs can be correlated in the frequency spectrum, polarisation, position-momentum, and spatial modes. Exploring the spatial modes' correlation has hitherto been limited to the polar coordinates' azimuthal angle, and a few attempts to study Walsh modes radial states. Here, we study the full-mode correlation, on a Laguerre-Gauss basis, between photon pairs generated in a type-I crystal. Furthermore, we explore the effect of a structured pump beam possessing different spatial modes onto bi-photon spatial correlation. Finally, we use the capability to project over arbitrary spatial mode superpositions to perform the bi-photon state's full quantum tomography in a 16-dimensional subspace.