Optical and Electron-Beam Spectroscopy of Single Solid-State Emitters - Towards Building Blocks for Coherent Optoelectronics

Solid-state single-photon emitters (SPEs) with controlled photon-number, polarization, and spectral mode are critical building blocks in coherent optoelectronics, an emerging area with transformative potential in quantum information processing and energy transduction.[1,2] However, our understanding of SPE structure-function relationships remains limited, and only a few classes of SPEs fulfill the stringent demands on stability, single-photon purity, and long optical coherence times set by applications in quantum optics. My talk highlights specific spectroscopic tools for assessing SPE photo-physics and identifies pathways for their rational chemical design.

First, I will demonstrate how a combination of photon-correlation spectroscopy and optical interferometry provides access to SPE optical coherences on timescales inaccessible with other spectroscopic techniques. Using this photon-correlation Fourier spectroscopy (PCFS), I show that individual lead-halide perovskite quantum dots (PQDs) at low temperatures display highly efficient single-photon emission with minimal spectral diffusion. I further identify remarkable optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210 picoseconds radiative lifetimes.[3,4] These measurements reveal that PQDs are the first colloidal semiconductor nanomaterial with potential application in quantum optics and present a starting point for the rational chemical design of lead halide perovskite-based SPEs [5] with fast emission, wide spectral tunability, and straightforward hybrid-integration with nanophotonic components. I will briefly touch on recent work on the optical control of detrimental charging dynamics in colloidal SPEs using ultrafast mid-infrared pulses.[6]

Second, I will show how scanning transmission electron microscopy (STEM) in conjunction with cathodoluminescence (CL) imaging can delineate structure-function relationships of established SPEs with sub-diffraction limited spatial resolution. We show that different sub-crystalline domains in nanodiamonds containing optically active silicon-vacancy centers (SiV) display changes in zero-phonon line (ZPL) energies and differences in brightness that we correlate with local lattice strain. Our results provide a comprehensive picture of the structural sources of inhomogeneous broadening of SiVs in diamond and demonstrate the utility of STEM-CL in studying critical SPEs photo-physics.[7]