Shot noise in transport through quantum dots: ballistic versus diffractive scattering

We investigate the shot noise in phase-coherent transport through quantum cavities by a two dimensional ab-initio simulation of the scattering problem. In particular, we study the influence of quantum scattering mechanisms on the transport statistics by tuning the strength of a disorder potential and the openings of the dot. For small cavity openings we find the shot noise for disordered samples to be of almost equal magnitude as for clean samples where transport is ballistic. We explain this finding by diffractive scattering at the cavity openings which act as strong noise sources. For ballistic cavities we demonstrate the emergence of "noiseless scattering states", irrespective of sharp-edged entrance and exit lead mouths. Our numerical results for the onset thresholds of these "classical" states are in very good agreement with analytical estimates.