Recovering quantum properties of continuous-variable states in the presence of measurement errors

TL;DR

This paper introduces a simple, efficient method to detect multipartite entanglement in continuous-variable quantum states despite measurement errors, by reconstructing physical covariance matrices and verifying entanglement conditions.

Contribution

It provides a novel approach to reliably identify entanglement in experimental data without complex optimizations, improving robustness against measurement errors.

Findings

Method to compute the best physical covariance matrix from measured data

Verification of entanglement using negativity of partial transposition

Demonstration on realistic experimental examples

Abstract

We present two results which combined enable one to reliably detect multimode, multipartite entanglement in the presence of measurement errors. The first result leads to a method to compute the best (approximated) physical covariance matrix given a measured non-physical one. The other result states that a widely used entanglement condition is a consequence of negativity of partial transposition. Our approach can quickly verify entanglement of experimentally obtained multipartite states, which is demonstrated on several realistic examples. Compared to existing detection schemes, ours is very simple and efficient. In particular, it does not require any complicated optimizations.