Generation of a GHZ State via Three-Photon Interference in Physically Separated Trapped Ion Nodes

Maximally entangled Greenberger-Horne-Zeilinger (GHZ) states are a cornerstone of quantum information processing, enabling advancements in quantum computing, communication, and metrology. Here, we report progress towards the creation of a three-qubit GHZ state between physically separated trapped ion qubit nodes, via three-photon interference. We use ¹³⁸Ba⁺ ground-state qubits and couple them to 493 nm optical qubits (photons), which are compatible with integrated photonic technologies and enable efficient photon collection through a high-NA lens into single-mode fibers. After collection, we interfere the photons through a beam-splitter setup and detect coincident three-photon events that herald a maximally entangled GHZ state in the three trapped ion qubits. This approach highlights the potential for scalable entanglement generation in distributed quantum networks via photonic links, paving the way for applications in quantum repeaters, distributed quantum computing, secure communications, and fundamental tests of quantum mechanics.