Revealing Hidden Coherence in Partially Coherent Light

TL;DR

This paper investigates how global transformations can convert correlations into coherence in partially coherent light, identifying optimal measures and quantifying the maximum coherence achievable from correlations.

Contribution

It introduces a method to quantify and maximize coherence extraction from correlations in partially coherent systems using global unitary transformations.

Findings

Global transformations can enhance coherence by converting correlations.

A measure for the correlations that can be turned into coherence is proposed.

Maximum achievable coherence from correlations is quantified.

Abstract

Coherence and correlations represent two related properties of a compound system. The system can be, for instance, the polarization of a photon, which forms part of a polarization-entangled two-photon state, or the spatial shape of a coherent beam, where each spatial mode bears different polarizations. Whereas a local unitary transformation of the system does not affect its coherence, global unitary transformations modifying both the system and its surroundings can enhance its coherence, transforming mutual correlations into coherence. The question naturally arises of what is the best measure that quantifies the correlations that can be turned into coherence, and how much coherence can be extracted. We answer both questions, and illustrate its application for some typical simple systems, with the aim at illuminating the general concept of enhancing coherence by modifying correlations.