Colloidal Quantum dots as Single Photon Quantum Emitters

The spectroscopic riddles of quantum confined colloidal quantum dots (CQDs) initially fueled synthetic advances following their birth at the end of the last millennium. As the 1990’s turned into the 2000’s, the synthesis had developed rapidly and commercial applications of CQDs emerged, first as bright and robust emitters for biological imaging, and later as the source of saturated green and red light in displays widely sold around the world. From the beginning the fluorescent properties of CQDs has been central to both their academic study as well as to their commercial success. As the tools to probe the photo-physics of individual CQDs have become more sophisticated, an appreciation of their properties as nano-emitters has grown. CQDs are now showing potential as quantum emitters, sources of single indistinguishable photons. It is this new direction that will be the focus of my presentation. Cesium lead halide perovskite CQDs, an emergent nano-material with unique optical properites, have now shown potential as colloidal sources of coherent single photons at cryogenic temperatures. We report that large CsPbBr3 CQDs (~20nm in size) show direct evidence of interference between indistinguishable single photons sequentially emitted from a single nanocrystal through Hong-Ou-Mandel interference in the absence of any radiative enhancement or photonic architecture.