Quantum and classical correlations of multiply scattered light

Abstract

Multiple scattering is a very common phenomenon since it occurs any time a wave meets a disordered medium. As almost any natural object has random structure in one form or another, the variety of the processes involving multiple scattering spans from electronic transport in solids to propagation of sound in a forest. In principle, multiple scattering is completely deterministic, and in the absence of absorption also reversible, which means that the information encoded into the incident wave can be perfectly recovered. However, in practice, due to its extreme complexity we often consider this process to be random, which leads to information loss. Within this approach correlations can be an important instrument of information recovery, because they directly quantify the amount of knowledge we get about the wave in a particular point from the measurement performed in a different point. In the first part of this thesis we study a novel type of mesoscopic correlations between the light intensities at the opposite sides of an opaque scattering slab. We study its dependence on the scattering medium properties and the incoming light beam parameters. In the last chapter of the first part we show how this correlation can be used to retrieve non-invasively the information about the shape of an object placed behind the scattering medium. In the second part we switch to the quantum aspects of the light propagation inside the scattering materials. We show that certain class of quantum correlations, quantum discord, can be present in the multimode output state of the scattered light even when the input light is in a thermal state, which is commonly considered classical. We propose a non-classicality measure based on the strength of this correlation, applying it to characterize the advantage due to the quantum measurement in discrimination of two coherent states in their mixture.