Towards entangling distributed registers of trapped ions

Our group is developing methods to entangle remote atomic registers, distributed over distances ranging from a few metres to hundreds of kilometres or more. Such atomic quantum networks could enable new applications in sensing, timekeeping, computing, and communication. Our approach employs network nodes, each comprising a trapped-ion register (⁴⁰Ca⁺), integrated with an optical cavity for efficient ion–photon coupling. Deterministic quantum logic within the register lets each node operate as a prototype photon-interfaced quantum processor.

I will summarise two recent results. First, we show how to entangle each ion qubit in a ten-ion register with a separate travelling photon [1]. By switching trap confinement, ions are sequentially brought into the cavity waist and emit photons via a laser-driven, cavity-mediated Raman transition, yielding a train of photonic qubits nearly maximally entangled in polarization with distinct ion qubits. The technique is directly scalable to larger ion-qubit registers and is a step towards entangling distributed networks of trapped-ion quantum processors, sensor arrays, and multi-ion clocks.

Second, we show how to programme the ion register to create multipartite entangled states of the emitted photons [2], specifically Greenberger–Horne–Zeilinger (GHZ) states of three path-switchable photons. These results show that established methods for preparing entangled states of co-trapped ions can be used to generate equivalent states of travelling photons, paving the way for efficient multipartite entanglement distribution and storage in future quantum local-area networks.

[1] M. Canteri et al., Photon‑interfaced ten‑qubit register of trapped ions, Phys. Rev. Lett. 135, 080801 (2025).

[2] M. Canteri et al,.  Generation of multipartite photonic entanglement using a trapped-ion quantum processing node, arXiv:2510.15693 (2025)