  Motivated by the experiments by Zrenner et al. [Nature 418, 612 (2002)], we
study the influence of relaxation processes on converting Rabi oscillations in
a strongly biased single-quantum-dot photodiode into deterministic
photocurrents. We show that the behavior of a quantum dot with different tunnel
rates for electron and holes is qualitatively different from that with the
equal tunnel rates: in the latter case the current shows attenuating
oscillations with the Rabi frequency. In contrast, for different electrons and
holes tunnelling rates, the frequency of these oscillations diminishes, and
they disappear beyond a definite asymmetry threshold. We give an analytical
solution of the problem and a numerical example showing a different behaviour
of the transferred charge in the small attenuation limit for equal and
different tunnel rates for electrons and holes.
