  Quantum dots (QDs) are one of the promising candidates of interconnection
between electromagnetic field and electrons in solid-state devices. Dark states
appear as a result of coherence between the electromagnetic fields and the
discrete energy levels of the system. Here, we theoretically solve the
steady-state solutions of the density matrix equations for a thee-level double
QD system and investigate the condition of the appearance of a dark state. We
also numerically show the appearance of the dark state by time-dependent
current characteristics.
