Solid-state quantum nodes based on color centers and rare-earth ions coupled with fiber Fabry–Pérot microcavities

High-performance optical quantum memories serving as quantum nodes are crucial for the distribution of remote entanglement and the construction of large-scale quantum networks. Notably, quantum systems based on single emitters can achieve deterministic spin–photon entanglement, which greatly simplifies the difficulty of constructing quantum network nodes. Among them, optically interfaced spins embedded in solid-state systems, as atomic-like emitters, are important candidate systems for implementing long-lived quantum memory due to their stable physical properties and robustness to decoherence in scalable and compact hardware. To enhance the strength of light-matter interactions, optical microcavities can be exploited as an important tool to generate high-quality spin–photon entanglement for scalable quantum networks. They can enhance the photon collection probability and photon generation rate of specific optical transitions and improve the coherence and spectral purity of emitted photons. For solid-state systems, open Fabry–Pérot cavities can couple single emitters that are not in proximity to the surface, avoiding significant spectral diffusion induced by the interfaces while maintaining the wide tunability, which enables addressing of multiple single emitters in the frequency and spatial domain within a single device. This review described the characteristics of single emitters as quantum memories with a comparison to atomic ensembles, the cavity-enhancement effect for single emitters and the advantages of different cavities, especially fiber Fabry–Pérot microcavities. Finally, recent experimental progress on solid-state single emitters coupled with fiber Fabry–Pérot microcavities was also reviewed, with a focus on color centers in diamond and silicon carbide, as well as rare-earth dopants.