Investigation of rare-earth ion-photon interaction and strong coupling in optical microcavities

Strong coupling between an emitter and a cavity is fundamental for quantum networks, enabling deterministic quantum state transfer, distributed quantum computing, and on-demand entanglement generation. Rare-earth ions (REIs) are a compelling candidate for such networks due to their long optical and spin coherence times. However, their inherently weak intra-4f optical transitions typically result in low coupling strengths, restricting most current achievements to the weak coupling regime. Our work proposes a realistic approach for achieving strong coupling between rare-earth ions and high-quality (Q) whispering-gallery-mode(WGM) microcavities. Our simulations further demonstrate that electro-optic tuning in this microdisk resonator system enables precise frequency alignment between rare-earth ions and the optical cavity mode across arbitrary target frequencies. Additionally, we provide numerical validation for a parametric amplification technique to enhance the emitter-cavity coupling strength. As an extension of this approach, the coupled system efficiently achieves the quantum entanglement of local and flying qubits. This study deepens the understanding of emitter–cavity interactions and contributes to realizing REIs-based photonic platforms, which are crucial to distributed quantum computing and developing robust quantum networks.