Abstract:   The advent of SPAD-array based parallelized detection of time-stamped single photons opens a pathway for extracting previously inaccessible spectroscopic information from dim sources of quantum light. In particular, it enables to multiplex detection both in time and in additional dimensions such as space, frequency or spatial frequency. We use this to study the interactions between pairs of excitons in doubly excited colloidal semiconductor nanocrystals, revealing weak multielectron effects at room temperature against a strong temperature broadened background. 

We present heralded spectroscopy [1], the unique identification and post-selection of pair emission events from single nanocrystals while performing a spectral measurement (using a line SPAD array [1]) or a defocused imaging measurement (using a 2D SPAD array [2]). Using this method we can characterize subtle differences between the first emitted photon (representing emission from the doubly excited state) and the second emitted photon (representing the singly excited state). Several examples for this will be given, including interaction effects on emission anisotropy from semiconductor nanorods [2] and identification of multiexcitonic states in quantum dot molecules [3]. The utility of our method for study of higher excited states via three-photon correlation and the potential for few-photon quantum sources at room temperature will also be discussed. 
 

References 
[1] G. Lubin et al., Nano Lett. 21, 6756 (2021) 
[2] D. Amgar et al., Nano letters, 23, 5417 (2023) 
[3] N. Frenkel et al., ACS Nano 17, 14990 (2023). 

Bio: Dan Oron is a professor at the department of Molecular Chemistry and Materials Science at the Weizmann institute, where he has held a PI position since 2007. His main research interests are at the interface between light and the nanoscale, studying both the interaction of light with nanostructured materials (mostly inorganic and hybrid semiconductor nanocrystals), optical superresolution methods based on measurements not associated with the intensity of scattered light, e.g. photon statistics or phase, and the optics of biological nanostructured materials and their biomimetic analogs.