Spreading Nonlocality in Quantum Network

TL;DR

This paper presents a protocol for distributing entanglement and nonlocal correlations across quantum networks using measurements on noisy states, enabling the creation of Bell-violating states in complex lattice structures.

Contribution

It introduces an optimal measurement-based scheme for entanglement distribution in 1D and 2D lattices, demonstrating superadditivity of nonlocality and device-independent verification.

Findings

Entanglement can be distributed in lattice networks with noise thresholds.

Bell-violating multipartite states can be generated from bipartite states.

Superadditivity of nonlocality observed in triangular lattices.

Abstract

Starting from several copies of bipartite noisy entangled states, we design a global and optimal local measurement-based protocol in one- and two-dimensional lattices by which any two or more prefix sites can be connected via entanglement. Production of bipartite as well as multipartite entangled states in a network is verified in a device independent way through the violation of Bell inequalities with two settings per site and with continuous range of settings. We also note that if the parties refuse to perform local measurements, the entanglement distribution scheme fails. We obtain critical values of noise allowed in the initial state so that the resulting output state show nonlocal correlation in different networks with arbitrary number of connections. We report that by employing our method, it is possible to create a Bell-violating multipartite entangled state from non-Bell violating bipartite states in an one-dimensional lattice with minimal coordination number being six. Such a feature of superadditivity in violation can also be observed in a triangular two dimensional lattice but not in a square lattice.