  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.
