Design of Silver Dimer-on-Mirror Nanocavities for Deterministically Positioned Quantum Emitters

Plasmonic nanocavities are widely used for enhancing the spontaneous emission rate, a key mechanism for developing efficient single-photon sources in quantum information and sensing. While past work focused on gold monomer-on-mirror cavities, here we explore plasmon-enhanced emission from silver dimer-on-mirror structures that are tailored for strain-induced quantum emitters, by using finite element simulations. Strain hotspots at the outer corners of nanocubes, created by stamping WSe₂ onto the structure, enable deterministic positioning of quantum emitters, as confirmed by scanning electron microscopy and simulations. The dimer, separated from a metal mirror by a dielectric gap, exhibits enhanced hybridized plasmonic modes, acting as a plasmonic tuning knob with strong field confinement in the gap and between the cubes, offering superior plasmonic features over monomers. Optimized design parameters such as gap thickness and dimer dimensions yield Purcell factors up to 1.3 × 10⁵ relative to vacuum, which corresponds to ≈1500 relative to the uncoupled state, i.e., the reference for experimental Purcell measurements without the planar metal mirror attached. Utilizing silver instead of the common gold mirror further reduces absorption losses at ultrathin gaps (∼5 nm), thereby increasing the Purcell factor to ≈2080, which is 4-fold enhanced compared to previous experimental values, while achieving a high quantum efficiency of ∼65-70%. Collection efficiency is estimated to range from 63 to 87%, or higher, depending on the optical setup. This scalable design offers a compact and tunable platform for efficient single-photon sources in quantum technologies.