Quantum and semiclassical polarization correlations

TL;DR

This paper compares quantum and semiclassical predictions for polarization correlations in light beams, showing that semiclassical models are limited to low visibility, unlike quantum states which can exhibit perfect correlations.

Contribution

It demonstrates the fundamental difference between quantum and semiclassical theories in polarization correlations, establishing a bound of 1/3 visibility for semiclassical models.

Findings

Semiclassical polarization correlations are bounded by 1/3 visibility.

Quantum states can exhibit 100% polarization correlations.

Experimental measurement confirms semiclassical limit in laser beams.

Abstract

We analyze the strength of polarization correlations between two light beams that can be achieved in the semiclassical regime using statistical mixtures of coherent states and binary on/off detectors. Under certain symmetry assumptions, the visibility of polarization correlations is shown to be bounded by 1/3, which is in a striking contrast with perfect 100% correlations exhibited by photon pairs prepared in the singlet state. The semiclassical limit is demonstrated in a measurement performed on a pair of laser beams undergoing correlated depolarization. This result illustrates the dramatic difference between predictions of quantum mechanics and the semiclassical theory of electromagnetic radiation for the polarization degree of freedom.