Keynote: Quantum Photonics at the Atomic Scale—Combined Optical and Electron Microscopy to Reveal, Create and Control Color Centers in 2D Materials and Nanoparticles

Bringing light to the transmission electron microscope promises to transform our understanding of quantum materials, enabling both observation of light-mediated processes and control of optical emission. This presentation will describe our efforts to probe and control color centers in both two dimensional materials and in diamond nanoparticles. First, we investigate color centers in hBN, a wide bandgap semiconductor with bright, room temperature quantum emission. Through high resolution transmission electron imaging, we find that multiple emitters are located within a diffraction-limited spot, each contributing to the observed quantum emission. We also find four unique classes of quantum emitters with distinct spectral signatures, each of which is strain-tunable. Next, we investigate quantum emission from individual nanodiamonds. Within larger nanoparticles (>100nm), we observe heterogeneity of emission, including a red-shifting of the 738nm SiV emission across the nanoparticle, and increased intensity of the phonon sideband. Interestingly, we see little change in emitter brightness at the surface of the nanodiamond compared to the bulk. Instead, distinct crystallites within the nanodiamond account for higher SiV emission heterogeneity more than surface structure and grain boundaries. We also show that a change in quantum yield is associated with a ZPL redshift and a 1% lattice expansion. This lattice strain is likely altering the electronic relaxation pathways, simultaneously affecting emitter brightness and zero phonon line energy. We hypothesize that crystal distortion is arising from multiple factors, including low angle grain boundaries, as well as variations in defect incorporation. Finally, within smaller nanoparticles (down to 1.7nm), we observe robust, single-defect emission. By combining atomic-scale imaging with AI, we help elucidate the atomic structure of individual quantum optical defects within sub-5nm nanodiamonds.