Complete analysis of measurement-induced entanglement localization on a three-photon system

TL;DR

This paper presents a theoretical and experimental study on how to localize and restore entanglement in a three-photon system after it is broken by environmental interactions, using polarization measurements and filters.

Contribution

It introduces a method for entanglement localization and enhancement after environmental coupling, applicable even when entanglement distillation fails.

Findings

Entanglement can be localized regardless of photon distinguishability.

Local polarization filters can increase entanglement beyond Bell inequality thresholds.

The technique restores entanglement where distillation does not.

Abstract

We discuss both theoretically and experimentally elementary two-photon polarization entanglement localization after break of entanglement caused by linear coupling of environmental photon with one of the system photons. The localization of entanglement is based on simple polarization measurement of the surrounding photon after the coupling. We demonstrate that non-zero entanglement can be localized back irrespectively to the distinguishability of coupled photons. Further, it can be increased by local single-copy polarization filters up to an amount violating Bell inequalities. The present technique allows to restore entanglement in that cases, when the entanglement distillation does not produce any entanglement out of the coupling.