  We demonstrate coherent control of a quantum dot exciton using photocurrent
detection with a sinusoidal reverse bias. Optical control is performed at low
bias, where tunneling-limited coherence times are long. Following this step,
the tunneling rates are increased to remove the long-lived hole, achieving a
high photocurrent signal. For a detection efficiency of 68%, electron and hole
tunneling times during optical control of 200 ps and 20 ns can be achieved,
compared to 120 ps and 7 ns for the constant bias case, respectively.
