Quantum probes to assess correlations in a composite system

TL;DR

This paper introduces an experimental method using quantum probes to efficiently assess correlations in a composite system by measuring only a small part, demonstrated on entangled photons with a focus on trace distance and angular correlations.

Contribution

It presents a novel strategy to infer system correlations through localized measurements using quantum probes, with a detailed analysis linking trace distance dynamics to angular correlations.

Findings

Quantum probes effectively reveal correlations in composite systems.

Trace distance increase correlates with angular correlations.

Method demonstrated on entangled photon pairs.

Abstract

We suggest and demonstrate experimentally a strategy to obtain relevant information about a composite system by only performing measurements on a small and easily accessible part of it, which we call quantum probe. We show in particular how quantitative information about the angular correlations of couples of entangled photons generated by spontaneous parametric down conversion is accessed through the study of the trace distance between two polarization states evolved from different initial conditions. After estimating the optimal polarization states to be used as quantum probe, we provide a detailed analysis of the connection between the increase of the trace distance above its initial value and the amount of angular correlations.