Exciton dephasing in quantum dots: Coupling to LO phonons via excited states

We have found a novel mechanism of spectral broadening and dephasing in quantum dots (QDs) due to the coupling to longitudinal-optical (LO) phonons. In theory, this mechanism comes into play only if the complete manifold of exciton levels (including those in the wetting-layer continuum) is taken into account. We demonstrate this nontrivial dephasing in different types of QDs, using the exactly solvable quadratic coupling model, here generalized to an arbitrary number of excitonic states.