Density-Matrix Theory with Renormalized Electron-Laser Coupling for Quantum-Dot Nonlinear Optical Response

A density-matrix theory has been employed for studying coherent electron dynamics in time-dependent occupation factors and induced quantum coherence for single and double quantum dots coupled to two incident laser fields. By introducing a self-consistent dynamical depolarization field, the renormalized light-electron interaction can be taken into account in connection with a quantum-mechanical exchange interaction between a pair of electrons within the same quantum dot. Moreover, the exchange interaction for two electrons in different quantum dots is also considered by applying the evanescent-field coupling based on a surface-plasmon model. In particular, the effect of quantum interference between two successively field-induced quantum coherences with respect to two lower and upper electronic states in a three-level quantum-dot system has been demonstrated, giving rise to a nonlinear optical response from indirect electron transition between the bottom and top energy levels.