Entanglement criteria for microscopic-macroscopic systems

TL;DR

This paper analyzes a micro-macro entanglement experiment, discussing the criteria used, the assumptions involved, and the potential for genuine entanglement detection despite losses, highlighting the importance of prior system knowledge.

Contribution

It critically evaluates the entanglement criterion used in a recent experiment and explores strategies for detecting genuine micro-macro entanglement under realistic loss conditions.

Findings

Entanglement can be inferred before losses under specific assumptions.

A fraction of the original entanglement persists despite losses.

Prior knowledge of the system is crucial for accurate entanglement detection.

Abstract

We discuss the conclusions that can be drawn on a recent experimental micro-macro entanglement test [F. De Martini, F. Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008). The system under investigation is generated through optical parametric amplification of one photon belonging to an entangled pair. The adopted entanglement criterion makes it possible to infer the presence of entanglement before losses, that occur on the macrostate, under a specific assumption. In particular, an a priori knowledge of the system that generates the micro-macro pair is necessary to exclude a class of separable states that can reproduce the obtained experimental results. Finally, we discuss the feasibility of a micro-macro "genuine" entanglement test on the analyzed system by considering different strategies, which show that in principle a fraction epsilon, proportional to the number of photons that survive the lossy process, of the original entanglement persists in any losses regime.