Partial Polarization by Quantum Distinguishability

TL;DR

This paper demonstrates that partial polarization in light beams can originate purely from quantum mechanical effects, specifically the distinguishability of photon paths, which affects the degree of polarization in a way classical theory cannot explain.

Contribution

The study provides both theoretical and experimental evidence that quantum distinguishability directly influences partial polarization, revealing a quantum origin of polarization correlations.

Findings

Degree of polarization depends on path distinguishability.

Erasable and inerasable distinguishability have different effects.

Classical theory cannot explain the quantum dependence observed.

Abstract

Partial polarization is the manifestation of the correlation between two mutually orthogonal transverse field components associated with a light beam. We show both theoretically and experimentally that the origin of this correlation can be purely quantum mechanical. We perform a two-path first-order (single photon) interference experiment and demonstrate that the degree of polarization of the light emerging from the output of the interferometer depends on path distinguishability. We use two independent methods to control the distinguishability of the photon paths. While the distinguishability introduced in one of the methods can be erased by performing a suitable measurement on the superposed beam, the distinguishability introduced in the other method cannot be erased. We show that the beam is partially polarized only when both types of distinguishability exist. Our main result is the dependence of the degree of polarization on the inerasable distinguishability, which cannot be explained by the classical (non-quantum) theory of light.