Quantum Correlation Imaging Through Scattering Media

Abstract

This thesis explores the use of spatially entangled photon pairs to enhance imaging contrast through weakly scattering media. Particular attention is paid to how the spatial correlations of biphotons survive or degrade on propagation through a scattering medium, and to how coincidence detection combined with post-selection on those correlations can separate ballistic from scattered light. Because ballistic biphotons preserve their source correlations while scattered pairs do not, retaining only the coincidences consistent with those correlations enhances contrast relative to conventional single-photon imaging and simultaneously rejects uncorrelated background. We demonstrate this enhancement, quantified through the modulation transfer function, in two configurations - one in which both photons from the pair are affected by the scattering medium, and one in which only a single photon is scattered while its partner follows an undisturbed reference path, directly to a spatially-resolving detector, which partially compensates for the resulting increase in shot noise by combining events from several post-selection windows.

In the first chapter, a brief overview of the field is provided, introducing the concept of contrast, the problem of scattering, and the degrees of freedom of light. The second chapter develops the background necessary to understand the experiment: the quantization of the electromagnetic field, quantum entanglement, spontaneous parametric down-conversion and the spatial and temporal correlations of the biphoton state, and the quantum imaging configurations that exploit them. In the third chapter, the experimental implementation and results are presented, followed by the article reporting the method and its demonstration through weakly scattering media. Finally, the conclusions and outlooks are outlined in the last chapter.