Fano-interference in an optical transition from a neutral quantum dot to a correlated many-body state

We investigate the effect of many-body interactions on the optical absorption spectrum of a charge-tunable quantum dot coupled to a degenerate electron gas. A constructive Fano interference between an indirect path, associated with an intra-dot exciton generation followed by tunneling, and a direct path, associated with the ionization of a valence-band quantum dot electron, ensures the visibility of the ensuing Fermi-edge singularity despite weak absorption strength. We find good agreement between experiment and renormalization group theory, but only when we generalize the Anderson impurity model to include a static hole and a dynamic dot-electron scattering potential. The latter is a consequence of the significant transient probability amplitude for intra-dot excitation and differentiates our work from earlier studies of X-ray absorption by an ensemble of deep-level states.