Two-Qubit Nanophotonic Quantum Network Node Using Strained Silicon-Vacancy Spins in Diamond

Quantum nodes incorporating a long-lifetime quantum memory and a high-fidelity spin-photon interface are a crucial component of long-range quantum networks. Here, we report on the deterministic creation of such nodes based on the ²⁹Si-isotope silicon-vacancy center (SiV) platform in diamond nanophotonic cavities, where the optically-accessible SiV electronic spin is combined with a reproducible nuclear spin memory qubit in an integrated two-qubit register. We demonstrate the necessary operations for a quantum network node, namely: spin-photon gates between the electron spin and a time-bin encoded photon, storage of the electron qubit state in the nuclear memory, and repeated electron initializations while preserving the nuclear memory. We perform these operations on a highly-strained SiV, leading to continued coherent operation even above typical dilution refrigerator temperatures, thus easing the way for a full implementation of the quantum repeater and entanglement distillation protocols between multiple nodes.