Permanent dipole moments improve quantum coherence near plasmonic structures

Plasmonic nanostructures enable strong, localized enhancement of electromagnetic fields, making them powerful platforms for mediating light interactions with quantum emitters (QEs) at the nanoscale. However, the spatial inhomogeneity of these fields imposes sub-nanometric precision requirements on emitter placement, limiting the robustness and scalability of quantum photonic systems. Here, we investigate how permanent dipole moments (PDMs) in polar QEs affect their optical response in such environments. In our model, PDMs introduce a nonlinear dependence of coupling strength and spontaneous emission rate on the local field amplitude. Our simulations of QEs near a plasmonic nanosphere show that PDMs can markedly reduce spatial variations in interaction strength and decay rate, yielding stabilized Rabi oscillations and extended coherence times even in strong-field gradients. Exploiting systems with PDMs thus offers a route to more robust QEs in confined optical fields, with potential benefits for quantum control, information processing, and nanophotonic device design.