Dynamics of electrons in a double quantum dot biased by an ac voltage: Nonlinear effect of Coulomb interaction

We investigate the dynamics of electrons in a double quantum dot biased by an ac voltage. For a closed system with two electrons, the exact diagonalization is performed on a many-body basis with the help of the time-evolution operator. We find three singlet states which show different dependences of quasienergies on the strength of Coulomb interaction $U$. The amplitude, as well as the nonlinear features, of the oscillation of the occupation number in a dot depends on the state and the value of $U$.