LOCALIZATION AND DELOCALIZATION OF AN ELECTRON IN BIASED AND UNBIASEDQUANTUM-WELLS DRIVEN BY A MONOCHROMATIC AND BICHROMATIC LASER FIELD

Localization (delocalization) of an electron driven by laser in a bias ed quantum well is considered. The initially trapped electron can be d elocalized by the field if the bias energy is close but not equal to a n integer number of a photon energy. When the bias energy is exactly e qual to an integer number of photon quanta, dynamical localization occ urs. A general analytical solution for a population difference is obta ined. When the electron is driven by a bichromatic field, localization regions are strongly dependent on the field incommensurability. The t opology of localization exhibits stable and unstable regions originati ng from nonanalytical behavior of the population with respect to the s mall incommensurability. This phenomenon resembles phase-transition in stabilities in the solid state. A low-frequency spectrum of electron o scillations consists of a low-frequency mode and split lines. We also show frequency controlling of the time evolution of an electron dipole moment on a phase shift between the two lasers. The low frequency can be increased or decreased, or it oscillates with the phase shift depe nding on the laser intensity.