Experimental observation of polarization coherence theorem

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.