# Experimental observation of polarization coherence theorem

## TL;DR

This paper reports the experimental verification of the polarization coherence theorem (PCT), demonstrating the fundamental relationship between polarization, coherence, and distinguishability in classical light fields using a Mach-Zehnder interferometer.

## Contribution

The first direct experimental observation of the polarization coherence theorem (PCT) for classical light fields, confirming the theoretical equality between polarization, coherence, and distinguishability.

## Key findings

- Confirmed PCT experimentally with classical light
- Used Mach-Zehnder interferometer for measurements
- Produced a complete gamut of polarization states

## Abstract

For light fields, the manifestation of correlations between fluctuating electric field components at different space-time points is referred to as coherence, whereas these correlations appearing between orthogonal electric field components at single space-time point are referred to as polarization. In this context, a natural question is: how coherence and polarization are interconnected? Very recently, a tight equality P^2=V^2+D^2 namely the "polarization coherence theorem" (PCT) connecting polarization P with interference visibility V (measure of coherence) and distinguishability D (measure of which-path information) has been proposed [Optica 4, 1113 (2017)]. We here report a direct observation of PCT for classical light fields using a Mach-Zehnder interferometer along with a synthesized source producing a complete gamut of degrees of polarizations. Our experimental demonstration could motivate ongoing experimental efforts towards probing the hidden coherences and complementarity features.