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A review of semiconductor-based schemes for the realization of quantum information processing devices is presented. After recalling the fundamentals of quantum information/computation theory, we shall discuss potential implementation schemes based on charge and/or spin degrees of freedom in semiconductor nanostructures. More specifically, we shall present an all-optical implementation scheme of quantum information processing with semiconductor macroatoms/molecules, where the computational degrees of freedom are interband optical transitions (excitonic states) manipulated/controlled by ultrafast sequences of multicolor laser pulses. We shall primarily focus on implementation schemes dealing with charge excitations in GaAs as well as GaN quasi-zero-dimensional structures. We shall finally discuss the possibility to combine charge and spin degrees of freedom, thus allowing for fast quantum gates which do not translate into fast decoherence times.

Strategies and concepts for the design of THz emitters based on the quantum cascade scheme are analyzed and modeled in terms of a fully three-dimensional Monte Carlo approach; this allows for a proper inclusion of both carrier-carrier and carrier-phonon scattering mechanisms. Starting from the simulation of previously published far-infrared emitters, where no population inversion is achieved, two designs are proposed. The first one follows the well-established chirped-superlattice scheme whereas the second one employs a double-quantum well superlattice to allow energy relaxation through optical phonon emission. For both cases a significant population inversion is predicted at temperatures up to 80 K. (C) 2001 American Institute of Physics.

Quantum cascade lasers in GaAs/AlGaAs heterostructures are operated in the THz range, with peak powers of several mWs and thresholds of few hundred A/cm/sup 2/ up to 60 K. Single-mode and continuous-wave emission are also achieved at 4.4 THz.