Benjamin P. Lanyon

The ability to establish entanglement between the nodes of future quantum networks is essential for enabling a wide range of new applications in science and technology. A promising approach involves the use of a powerful central node capable of deterministically preparing arbitrary multipartite entangled states of its matter-based qubits and efficiently distributing these states to surrounding end nodes via flying photons. This central node, referred to as a ``factory node", serves as a hub for the production and distribution of multipartite entanglement. In this work, we demonstrate key functionalities 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 entanglement witnesses. These photons can, in the future, be used to establish stored multipartite entanglement between remote matter-based nodes. Our results demonstrate that the well-established techniques for the deterministic preparation of entangled states of co-trapped ion qubits can be used to prepare the same states of traveling photons, paving the way for multipartite entanglement distribution in quantum local area networks.

We explore trapped ions as a setting to investigate non-equilibrium phases in a generalised Dicke model of dissipative spins coupled to phonon modes. We find a rich dynamical phase diagram including superradiant-like regimes, dynamical phase-coexistence and phonon-lasing behaviour. A particular advantage of trapped ions is that these phases and transitions among them can be probed in situ through fluorescence. We demonstrate that the main physical insights are captured by a minimal model and consider an experimental realisation with Ca+ ions trapped in a linear Paul trap.