Coupling symmetry of quantum dot states

With noninvasive methods, we investigate ground and excited states of a lateral quantum dot. Charge detection via a quantum point contact is used to map the dot dynamics in a regime where the current through the dot is too low for transport measurements. In this way we investigate and compare the tunneling rates from the dot to source and drain. We find a symmetry line on which the tunneling rates to both leads are equal. In this situation ground states as well as excited states influence the mean charge of the dot. A detailed study in this regime reveals that the coupling symmetry depends on the number of states contributing to transport and on the spatial distribution of individual states.