Single-photon sources are required for quantum technologies and can be created from individual atoms and atom-like defects. Erbium ions produce single photons at low-loss fiber optic wavelengths, but they have low emission rates, making them challenging to isolate reliably. Here, we tune the size of gold double nanoholes (DNHs) to enhance the emission of single erbium emitters, achieving 50× enhancement over rectangular apertures previously demonstrated. This produces enough enhancement to show emission from single nanocrystals at wavelengths not seen in our previous work, i.e., 400 and 1550 nm. We observe discrete levels of emission for nanocrystals with low numbers of emitters and demonstrate isolating single emitters. We describe how the trapping time is proportional to the enhancement factor for a given DNH structure, giving us an independent way to measure the enhancement. This shows a promising path to achieving single emitter sources at 1550 nm.

Nanohole optical tweezers have been used by several groups to trap and analyze proteins. In this work, we demonstrate that it is possible to create high-performance double nanohole (DNH) substrates for trapping proteins without the need for any top-down approaches (such as electron microscopy or focused-ion beam milling). Using polarization analysis, we identify DNHs as well as determine their orientation and then use them for trapping. We are also able to identify other hole configurations, such as single, trimers and other clusters. We explore changing the substrate from glass to polyvinyl chloride to enhance trapping ability, showing 7 times lower minimum trapping power, which we believe is due to reduced surface repulsion. Finally, we present tape exfoliation as a means to expose DNHs without damaging sonication or chemical methods. Overall, these approaches make high quality optical trapping using DNH structures accessible to a broad scientific community.

Scalable methods to access single-photon sources on demand are highly sought after. As a potential strategy, we demonstrate the optical trapping and chemical anchoring of NaYF 4 nanoparticles (NPs) and NaYF 4 NPs doped with on average a single Er 3+ ion. The anchoring method we present involves surface coating the NPs with thiol-functionalized phospholipids, where the thiol group is protected with a chemical group photoremovable at 340 nm 2-bromo-4′-hydroxyacetophenone. Functionalized NPs are trapped optically in a gold double-nanohole aperture using a 980 nm laser. A 340 nm light beam is focused on the particle, resulting in deprotection of the thiol groups and attachment of the thiols to the gold surface, permanently anchoring the NPs. Electron microscopic imaging proves the successful anchoring after removal of the trapping laser, 340 nm light source, and solvent. The approach is promising for reliably fabricating a single-photon emitting material in a scalable and potentially automatable manner.

Gap plasmon structures could enable future ultrafast communication by allowing simultaneous nanoscale integration of electromagnetic waves, nonlinear and optical-electrical conversion, and providing a critical element often overlooked in this context: electrical contacts. Here, the fundamental limit of these structures is discussed, and it is argued that the conventional concept of “smaller is better" for higher confinement is not true when the loss is considered, but few nanometer gaps will be required to give the best performance. Overall, to achieve widescale adoption, plasmonics will likely have to combine forces with emerging CMOS-like nanophotonics.

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