Quantum Networking at the Speed of Quantum Computation: Kilohertz Entanglement in a Heterogeneous Quantum System

Abstract: Distributed quantum computing requires rapid, high-fidelity entanglement between qubits in separate processor modules. Photonic links between single-atom qubits provide switchable, long-range connections, but photon loss limits their entanglement rate. Here we entangle a trapped $<sup>{138}$Ba$<sup>{+}$ ion with a silicon-vacancy (SiV$<sup>{-}$) center in a diamond nanophotonic cavity. A photon emitted by the ion is converted in wavelength and encoding, reflected from the SiV$<sup>{-}$--cavity system and detected, so that a single detected photon heralds entanglement. Including all conversion losses, we generate ion--SiV$<sup>{-}$ Bell pairs at an average rate of 1.03(1)\,kHz with a fidelity of 87.9(7)\%. This is four times the rate of the fastest photonic link between two trapped ions and corresponds to one Bell pair per millisecond, matching the cycle time of planned trapped-ion processors.