Nonlinear Intersubband Photoabsorption in Asymmetric Single Quantum Wells

A density-matrix approach combined with time-dependent density-functional theory is used to calculate the intersubband photoabsorption in a strongly driven, DC-biased GaAs/AlGaAs single quantum well. For certain frequencies and intensities of the driving field, optical bistability is observed. Compared to a full time propagation of the density matrix, the commonly used two-level rotating wave approximation becomes less and less accurate for increasing asymmetry.