Remote Entanglement of Single Rare-earth Ion Qubits Coupled to Nanophotonic Cavities

Solid state emitters are a promising platform for building quantum repeater networks for long-range entanglement distribution, enabling applications such as secure communication, distributed quantum computing and non-local sensing. Scaling-up current lab-based networks requires increased quantum link efficiencies, fidelities and complexities. However, the spatial and temporal variation of optical transition frequencies in solid state systems has hindered progress.

We introduce a novel approach to entanglement generation that uses frequency erasing photon detection combined with real-time quantum control based on feedforward of photon detection times. This protocol eliminates the deleterious effect of dynamic optical inhomogeneity, whilst leveraging static inhomogeneity for frequency-multiplexed entanglement distribution.

We demonstrate entanglement of single rare-earth ion qubits in solid state hosts (¹⁷¹Yb:YVO₄) coupled to two remote nanophotonic cavities. We herald two-qubit Bell States using a single-photon detection with fidelities of 0.723 at rates of 3.1Hz. Two-photon protocols boost the fidelity to 0.84 at the cost of a reduced 17mHz rate. Furthermore, we prepare and analyze tripartite entangled W-states of three optically distinguishable ¹⁷¹Yb qubits.

These results demonstrate the intrinsic scalability and robustness of our combined quantum-networking platform and protocol, laying the foundation for the future quantum internet.