  We theoretically investigate the tunneling-induced transparency (TIT) and the
Autler-Townes (AT) doublet and triplet in a triple-quantum-dot system. For the
resonant tunneling case, we show that the TIT induces a transparency dip in a
weak-tunneling regime and no anticrossing occurs in the eigenenergies of the
system Hamiltonian. However, in a strong-tunneling regime, we show that the TIT
evolves to the AT splitting, which results in a well-resolved doublet and
double anticrossings. For the off-resonance case, we demonstrate that, in the
weak-tunneling regime, the double TIT is realized with a new detuning-dependent
dip, where the anticrossing is also absent. In the strong-tunneling regime, the
AT triplet is realized with triple anticrossings and a wide detuning-dependent
transparency window by manipulating one of the energy-level detunings. Our
results can be applied to quantum measurement and quantum-optics devices in
solid systems.
