  We perform two-dimensional coherent spectroscopy on CdSe/CdZnS core/shell
colloidal quantum dots at cryogenic temperatures. In the two-dimensonal
spectra, sidebands due to electronic coupling with CdSe lattice LO-phonon modes
are observed that have evolutions deviating from the exponential dephasing
expected from Markovian spectral diffusion. Comparison to simulations provides
further evidence that the LO-phonon mode coupling itself significantly modifies
the exciton lineshapes and results in the underlying spectral diffusion on
ultrafast timescales.
