Characterizing the multipartite continuous-variable entanglement structure from squeezing coefficients and the Fisher information

TL;DR

This paper uses quantum metrology techniques to analyze the entanglement structure of multimode continuous-variable states, providing insights into their robustness and separability across various partitions.

Contribution

It introduces a method to microscopically characterize multipartite entanglement in continuous-variable systems using squeezing coefficients and Fisher information.

Findings

Demonstrates the effectiveness of metrological sensitivity in detecting entanglement.

Provides bounds for separability in different partitions of Gaussian states.

Shows robustness of cluster-state entanglement under photon losses.

Abstract

Understanding the distribution of quantum entanglement over many parties is a fundamental challenge of quantum physics and is of practical relevance for several applications in the field of quantum information. Here we use methods from quantum metrology to microscopically characterize the entanglement structure of multimode continuous-variable states in all possible multi-partitions and in all reduced distributions. From experimentally measured covariance matrices of Gaussian states with 2, 3, and 4 photonic modes with controllable losses, we extract the metrological sensitivity as well as an upper separability bound for each partition. An entanglement witness is constructed by comparing the two quantities. Our analysis demonstrates the usefulness of these methods for continuous-variable systems and provides a detailed geometric understanding of the robustness of cluster-state entanglement under photon losses.