Generation of multipartite photonic entanglement using a trapped-ion quantum processing node

The ability to establish entanglement between the nodes of future quantum networks is essentialfor enabling a wide range of new applications in science and technology. A promising approach in-volves the use of a powerful central node capable of deterministically preparing arbitrary multipartiteentangled states of its matter-based qubits and efficiently distributing these states to surrounding endnodes via flying photons. This central node, referred to as a “factory node”, serves as a hub for theproduction and distribution of multipartite entanglement. In this work, we demonstrate key func-tionalities of a factory node using a cavity-integrated trapped-ion quantum processor. Specifically,we program the system to generate genuinely multipartite entangled Greenberger-Horne-Zeilinger(GHZ) states of three path-switchable photons and verify them using custom-designed entanglementwitnesses. These photons can, in the future, be used to establish stored multipartite entanglementbetween remote matter-based nodes. Our results demonstrate that the well-established techniquesfor the deterministic preparation of entangled states of co-trapped ion qubits can be used to preparethe same states of traveling photons, paving the way for multipartite entanglement distribution inquantum local area networks.