Revealing Long Dephasing Time Properties on CdSe\ZnSe Strain-Graded Quantum Dots with Multidimensional Optical Nonlinear Spectroscopy

In recent years, semiconductor quantum dots have become a well-established class of material for numerous applications, mainly due to their set of tunable optical properties. As a strategy to gain further control over their excitonic properties, different types of core\shell heterostructures have been developed. Within those, strain-graded CdSe\ZnSe core-\shell has been explored as an alternative to gain control over exciton-phonon interactions, enabling suppression of this process, which can result in longer coherences and narrower emission spectrum. Here, using a multidimensional coherent spectroscopy system, we investigate the effect of strain on the exciton-phonon interaction on a series of wurzite CdSe\ZnSe heterostructures. We show that the suppressed interaction reduces the homogeneous linewidth to nearly 10 meV at room temperature, which corresponds to the longest exciton coherence time measured for colloidal nanoparticles at room temperature, and about one order of magnitude longer than for regular CdSe-based core\shell heterostructures. With the increasing demand for materials with long coherence time, especially for quantum information applications, the ten-fold enhancement of the coherence time observed for these strain-graded nanomaterials makes this class of heterostructure a new promising platform for quantum information applications.