Quantum states of light in hybrid 2D material-nanophotonic systems

Abstract

Layered van der Waals materials are held together with strong in-plane bonds and weak out-of-plane van der Waals forces, permitting facile exfoliation into monolayers. One particularly interesting class of van der Waals materials is transition metal dichalcogenides, mainly monolayer WSe2, which has been shown to host quantum states of light that emit single photons at cryogenic temperatures in regions of tensile strain. These single-photon emitters have a broad range of applications in emergent quantum technologies, but understanding the formation, placement, and control of these states has proven difficult and attracted a large amount of research attention. Here, the work in this dissertation investigates single photon emission in monolayer WSe 2 via integration with nanophotonic structures. One such platform is nanoindentation, where WSe 2 placed on a polymer substrate is deformed using a sharp atomic force microscopy tip to induce single photon emitters. An open question is whether the delicate WSe 2 tears or remains intact after nanoindentation. This work presents a nanoinversion technique that converts nanoindents into protruding Au pillars that permit metrological analysis of the WSe 2 to identify tears and conclude that, regardless of tearing, single photon emitters persist. It is also reported in this dissertation that single photon emitters at nanoindentation sites can be selectively brightened through the addition of a capping graphite layer, quenching broadband defect emission. However, localized defects have been theorized to play a major role in WSe 2-based single photon emission. Because of high defect densities, to conclusively validate this theory, one must correlate room temperature defect emission with cryogenic single photon emission using near-field optical spectroscopy. Cryogenic near-field spectroscopy is exceedingly difficult and only exists in a small number of laboratories around the world. To address this limitation, this dissertation reports the fabrication of integrated near-field antennas into the substrate of a WSe 2 flake that selectively enhances single photon emitters above its apex. By then identifying the localization of emitters to spatial regions around the apex of the probe using localization spectroscopy and photoluminescent excitation spectroscopy, this platform can enable correlation between cryogenic single photon emission and room temperature defect emission for the first time.