Quantum limits to polarization measurement of classical light

TL;DR

This paper calculates the fundamental quantum limit to the precision of polarization measurements of classical light, revealing the impact of quantum mechanics on measurement accuracy and proposing methods to approach this limit.

Contribution

It explicitly derives the quantum limit for polarization measurement of classical light and demonstrates how conventional receivers can nearly achieve this bound.

Findings

Quantum limit derived for polarization measurement precision

Optimal measurement strategies identified for classical light

Conventional receivers can approach the quantum limit

Abstract

Polarization of light is one of the fundamental concepts in optics. There are many ways to measure and characterise this feature of light but at the fundamental level it is quantum mechanics that imposes ultimate limits to such measurements. Here, I calculate the quantum limit to a precision of a polarization measurement of classical coherent light. This is a multiparameter estimation problem with a crucial feature of noncommuting optimal observables corresponding to each parameter which prohibits them to be measured at the same time. I explicitly minimize the quantum Holevo-Cramer-Rao bound which tackles this issue and show that it can be locally saturated by two types of conventional receivers.