Internal photoeffect from a single quantum emitter

We demonstrate by time-resolved resonance fluorescence measurements on a single self-assembled quantum dot an internal photoeffect that emits electrons from the dot by an intraband excitation. We find a linear dependence of the optically generated emission rate on the excitation intensity and use a rate equation model to deduce the involved rates. The emission rate is tunable over several orders of magnitude by adjusting the excitation intensity. Our findings show that a process that is well known in single atom spectroscopy (i.e., photoionization) can also be observed in the solid state. The results also quantify an important, but mostly neglected, mechanism that may fundamentally limit the coherence times in solid-state quantum optical devices.