Nonlinear dynamics in multisubband semiconductor quantum wells under terahertz radiation

Coherent control of subband transition in multisubband semiconductor nanostructures under a cw terahertz field has been investigated. An additional ultrafast-infrared pulse is applied to excite electrons in the conduction subbands of semiconductor quantum wells. Our simulation is based on the semiconductor Bloch equations including three conduction subbands. Since the subband energy difference is small, rotating wave approximation will be avoided. Our results indicate that terahertz field intensity and phase conditions have great impact on the response to the excitation. The subband population is sensitive to phase difference of the terahertz field and the external ultrafast-infrared pulse. The excited electrons can be modulated by the phase conditions of the terahertz field. Nonlinear optical absorption under different terahertz field intensities is explored. Two optical absorption peaks which correspond to transitions between the ground level and the upper two subbands, show red shifts with increasing terahertz field intensity. At the same time, the first absorption peak increases while the second one decreases with the growth of the terahertz radiation intensity