Optical properties of artificially generated carbon-related quantum emitters in hexagonal boron nitride

Hexagonal boron nitride (hBN), a two-dimensional wide-bandgap material, has emerged as a promising host for optically stable quantum emitters (QEs) suitable for quantum photonic and sensing applications. This dissertation investigates the controlled fabrication, optical characterization, and robustness of carbon-related single-photon emitters (SPE) in hBN, with an emphasis on their integration into chip-scale quantum devices.

In this work, several previously reported fabrication methods have been studied, which include focused ion beam (FIB), Reactive Ion Etching (RIE), Inductively Coupled Plasma (ICP) RIE, liquid exfoliation, and sputtered carbon. However, each method lacks one or more key attributes required for realizing an ideal, chip-integrable quantum emitter. Thus, a reproducible, contamination minimizing fabrication method is developed using atomic force microscopy (AFM) nanoindentation with diamond-like carbon-coated tips, introducing carbon impurities into the hBN lattice in a spatially controlled manner. The resulting emitters exhibit deterministic positioning and strong spectral similarity, indicating the successful and repeatable creation of a specific emitter class. ... mehrExtensive photophysical analysis of over 300 emitters reveals a narrow distribution of zero-phonon lines (ZPLs), primarily in between \SI{565}{\nano\meter} to \SI{590}{\nano\meter} range. The emitters are attributed to carbon-trimer defects, specifically the C₂C$_N$ configuration, supported by theoretical comparisons.

The environmental stability of these emitters is assessed through molecular deposition of TbPc₂, a single-molecule magnet. The emitters remain optically active and show enhanced ZPL intensity upon molecular deposition, demonstrating their robustness against external perturbation—an essential criterion for quantum sensing.

Furthermore, advanced spectroscopic techniques including photoluminescence excitation (PLE) spectroscopy and room-temperature optically detected magnetic resonance (ODMR) are employed to probe the electronic structure of the emitters. While limited spin contrast is observed under ODMR, PLE measurements reveal lifetime-limited linewidths for selected emitters, confirming their high optical quality.

This work lays the foundation for the scalable integration of hBN-based quantum emitters into hybrid quantum technologies by addressing key challenges in emitter creation, stability, and spectral purity.