Quantum degrees of polarization

TL;DR

The paper reviews various quantum polarization measures, highlighting their differences and limitations, and suggests multiple measures may be needed for different applications in quantum optics.

Contribution

It compares different quantum degrees of polarization, analyzing their properties and differences, and discusses the limitations of classical analogies in quantum contexts.

Findings

Different quantum polarization measures order states differently.

Classical Stokes operator analogy is insufficient for quantum polarization.

Multiple measures may be necessary for comprehensive characterization.

Abstract

We discuss different proposals for the degree of polarization of quantum fields. The simplest approach, namely making a direct analogy with the classical description via the Stokes operators, is known to produce unsatisfactory results. Still, we argue that these operators and their properties should be basic for any measure of polarization. We compare alternative quantum degrees and put forth that they order various states differently. This is to be expected, since, despite being rooted in the Stokes operators, each of these measures only captures certain characteristics. Therefore, it is likely that several quantum degrees of polarization will coexist, each one having its specific domain of usefulness.