ABSTRACT
Coherent manipulation of quantum states is a critical step toward many
novel technological applications ranging from manipulation of qubits in
quantum logic gates [1-5] to controlling the reaction pathways of molecules.
In the field of the quantum state control by optical means, both Rabi os-
cillation and quantum interference play the central roles. The exciton Rabi
splitting was observed in the luminescence spectrum of a single InGaAs
quantum dot and the exciton Rabi oscillation was also observed in the
spectroscopy of a single GaAs or InGaAs quantum dot [6-12]. The two-
qubit CROT gate operation was demonstrated using two orthogonally po-
larized exciton states and a biexciton state in a GaAs quantum dot [13].
Unfortunately, however, the decoherence/dephasing times of excitons and
biexcitons in these quantum dots are limited by the radiative lifetimes (∼ 1 ns) even at low temperatures. Thus a qubit with a longer decoherence
time is desirable for the application to the quantum information process-
ing. Electron spins in semiconductor quantum dots(QDs) are considered as
one of the most promising candidates of the building blocks for quantum
information processing [14, 15] due to their robustness against decoherence
effects [16, 17]. In double QD systems, initialization and coherent manipu-
lation of electron spin have been realized, with coherence times extending
to 1 µs [18, 19].
