Single quantum dot photodiodes: Rabi-flops in a two level system with electric contacts

On the basis of a single semiconductor quantum dot incorporated in a photodiode we have succeeded in preparing a two-level system with electric contacts, a setup which was previously not attained on the basis of other two-level systems. By means of such a single quantum dot photodiode we demonstrate the transfer of coherent optical excitations into deterministic photocurrents. Rabi oscillations are shown to be directly reflected in the photocurrent. For optical excitation with pi-pulses we observe a quantitative photocurrent given by I=f /spl times/ e, where f is the repetition frequency of the experiment and e is the elementary charge.