Quantum-Memory-Enhanced Preparation of Nonlocal Graph States

TL;DR

This paper presents a method to efficiently generate large-scale multipartite entangled graph states using atomic quantum memories, overcoming previous exponential efficiency decay in linear optics schemes.

Contribution

It introduces a polynomial-overhead scheme for preparing graph states with atomic memories, enabling scalable quantum networks and distributed quantum information processing.

Findings

Successfully generated a four-photon GHZ state with high fidelity.

Demonstrated violation of Bell inequalities using the generated state.

Showcased applications in quantum cryptography and quantum metrology.

Abstract

Graph states are an important class of multipartite entangled states. Previous experimental generation of graph states and in particular the Greenberger-Horne-Zeilinger (GHZ) states in linear optics quantum information schemes is subjected to an exponential decay in efficiency versus the system size, which limits its large-scale applications in quantum networks. Here we demonstrate an efficient scheme to prepare graph states with only a polynomial overhead using long-lived atomic quantum memories. We generate atom-photon entangled states in two atomic ensembles asynchronously, retrieve the stored atomic excitations only when both sides succeed, and further project them into a four-photon GHZ state. We measure the fidelity of this GHZ state and further demonstrate its applications in the violation of Bell-type inequalities and in quantum cryptography. Our work demonstrates the prospect of efficient generation of multipartite entangled states in large-scale distributed systems with applications in quantum information processing and metrology.