Optical Coherence Time of CdSe Nanoplatelets

Optical quantum technologies are dependent on quantum emitters with near-perfect optical coherences, meaning highly efficient single-photon emission with long coherence times. CdSe Nanoplatelets (NPLs) present as a promising material for quantum emitters due to their high photoluminescence quantum yields, tunable emission energies, narrow size distribution and fast radiative lifetimes. Compared to their colloidal quantum dot analogues, NPLs feature order of magnitude faster radiative lifetimes at cryogenic temperatures, meaning much more efficient photon emission. However, to fully understand their potential as quantum emitters, understanding of their optical dephasing processes, and their coherence times, at cryogenic temperatures is necessary. Dephasing can occur due to a variety of processes including scattering with phonons, relaxation from multiple fine structure states, and interactions with charges resulting in spectral diffusion. To understand the dephasing mechanisms, single particle studies are necessary to avoid obfuscation that occurs with ensemble inhomogeneities. At the single particle level, conventional fluorescence techniques are limited due to low photon counts reducing the temporal resolution, and finite dispersing power of the spectrometer restricting the frequency resolution. To extend beyond these limits, we used photon correlation Fourier spectroscopy. Photon correlation Fourier spectroscopy allows for increased spectral and temporal resolution by combining the high temporal resolution of photon correlation spectroscopy and high frequency resolution of Fourier spectroscopy. Here, intensity correlations are measured at different interferometer positions, while dithering a mirror, to get a time dependent spectral correlation function. Here, we have used this unique technique on single particle CdSe NPLs, extract the spectral line shape, emitter dynamics, and lower bound for their optical decoherence time.