  Quantum computing (or generally, quantum information processing) is of prime
interest for it potentially has a significant impact on present electronics and
computations1-5. Essence of quantum computing is a direct usage of the
superposition and entanglement of quantum mechanical states that are pronounced
in nanoscopic particles such as atoms and molecules6, 7. On the other hand,
many proposals regarding the realization of semiconductor quantum dot (QD)
qubits8,9 and QD quantum gates10 were reported and several experimental clues
were successfully found11-16. While these pioneering experiments opened up the
basis of semiconductor QD quantum computing, direct electrical control of
superposed states in time domain17 has not been realized yet. Here, we
demonstrate the coherent control of the superposed quantum states evolution in
the QD molecule. Short electrical pulses are shown to inject single electron
into the QD molecule and the current collected at the substrate exhibits
oscillations as a function of the pulse width. The oscillations are originated
from different decay rates of the symmetric (S) and the anti-symmetric (AS)
state of the QD molecule and the evolution of the occupation probabilities
controlled by the injection pulse width
