Bimodal statistic on a single dot device

We explore the full counting statistics of single electron tunneling through a quantum dot using a quantum point contact as non-invasive high bandwidth charge detector. The distribution of counted tunneling events is measured as a function of gate and source–drain-voltage for several consecutive electron numbers on the quantum dot. For bias voltages at which excited states become accessible we find a bimodal characteristic of the counting distribution. The bimodal distribution arises from a slow switching between different electron configurations on the dot. To characterize the switching process we analyze the time dependence of the number of electrons passing the dot in a given time.