Scalable Multipartite Entanglement of Remote Rare-earth Ion Qubits

Single photon emitters with internal spin are leading contenders for developing quantum repeater networks, enabling long-range entanglement distribution for transformational technologies in communications and sensing. However, scaling beyond current few-node networks will require radical improvements to quantum link efficiencies and fidelities. Solid-state emitters are particularly promising due to their crystalline environment, enabling nanophotonic integration and providing spins for memory and processing. However, inherent spatial and temporal variations in host crystals give rise to static shifts and dynamic fluctuations in optical transition frequencies, posing formidable challenges in establishing large-scale, multipartite entanglement. Here, we introduce a scalable approach to quantum networking that utilizes frequency erasing photon detection in conjunction with adaptive, real-time quantum control. This enables frequency multiplexed entanglement distribution that is also insensitive to deleterious optical frequency fluctuations. Single rare-earth ions are an ideal platform for implementing this protocol due to their long spin coherence, narrow optical inhomogeneous distributions, and long photon lifetimes. Using two 171Yb:YVO4 ions in remote nanophotonic cavities we herald bipartite entanglement and probabilistically teleport quantum states. Then, we extend this protocol to include a third ion and prepare a tripartite W state: a useful input for advanced quantum networking applications. Our results provide a practical route to overcoming universal limitations imposed by non-uniformity and instability in solid-state emitters, whilst also showcasing single rare-earth ions as a scalable platform for the future quantum internet.