Experimental demonstration of a fully inseparable quantum state with nonlocalizable entanglement

TL;DR

This paper demonstrates the existence of fully inseparable three-qubit quantum states with nonlocalizable entanglement, both theoretically and experimentally, highlighting their potential significance in quantum information processing.

Contribution

It introduces a family of fully inseparable states with nonlocalizable entanglement and provides the first experimental demonstration of such states using linear optics.

Findings

Nonlocalizable entanglement exists in mixtures of GHZ states and white noise.

A two-parameter family of such states is characterized.

Experimental verification confirms theoretical predictions.

Abstract

Localizability of entanglement in fully inseparable states is a key ingredient of assisted quantum information protocols as well as measurement-based models of quantum computing. We investigate the existence of fully inseparable states with nonlocalizable entanglement, that is, with entanglement which cannot be localized between any pair of subsystems by any measurement on the remaining part of the system. It is shown, that the nonlocalizable entanglement occurs already in suitable mixtures of a three-qubit GHZ state and white noise. Further, we generalize this set of states to a two-parametric family of fully inseparable three-qubit states with nonlocalizable entanglement. Finally, we demonstrate experimentally the existence of nonlocalizable entanglement by preparing and characterizing one state from the family using correlated single photons and linear optical circuit.