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The screened Coulomb-phonon quantum kinetics is applied to the twopulse excitation of femtosecond four-wave mixing (FWM). The time-resolved FWM shows, both in theory and experiment, a characteristic photon echo structure. From the analysis of the theoretical and experimental time-integrated signal, a dephasing time is obtained which varies with the inverse cubic power of the plasma density. Finally, FWM with coherent control yields in theory and experiment coherent plasmon-phonon mixed mode quantum beats. [ABSTRACT FROM AUTHOR]

The two-time screened Coulomb potential, as it results from a selfconsistent solution of the full Coulomb quantum kinetics after a femtosecond optical pulse, is described. The resulting potential is compared to femtosecond—resolved optical pump and THz—probe measurements including also the screening of the phonon-assisted carrier-carrier interaction. Excellent agreement between experiment and theory is found. Finally, the predictions of the Coulomb quantum kinetics for femtosecond four-wave mixing without and with coherent control are compared to corresponding experiments resulting in a density-dependent dephasing time and plasmon-phonon quantum beats. [ABSTRACT FROM AUTHOR]

The quantum kinetics for Coulomb interactions is derived. It is shown that the screened scattering potential depends on two time arguments, because screening is built up only after the carriers have been excited and begin to rearrange. The nonequilibrium screened Coulomb potential obeys an integral equation with a polarization due to carrier-carrier scattering. By a generalization of the equilibrium theory, a time-dependent plasmon-pole approximation is derived in order to illustrate the physical content of the complex formalism. [ABSTRACT FROM AUTHOR]

The full wealth of quantum kinetics can be tested by time-resolved femtosecond two-pulse spectroscopy either in the form of pump-probe spectroscopy or in the form of four-wave mixing. It is shown that pump-probe spectroscopy is amenable to follow the temporal evolution of the particle distributions. This is illustrated by calculations and experiments on the buildup of phonon cascades and on non-Markovian relaxation scenarios. Four-wave mixing, on the other hand, is shown to be well-suited for the study of quantum coherence and its dephasing illustrated by LO-phonon quantum beats. [ABSTRACT FROM AUTHOR]

The interband quantum kinetics is formulated for the scattering of the excited electrons and holes by a thermal bath of optical phonons. A series of approximations is developed for the required retarded functions, including a discussion of the band splitting introduced by a resonant intense laser beam. It is shown that the damping by LO-phonons can be described well with a hyperbolic secant. Finally strategies for the numerical solutions of the quantum kinetic equations are discussed. [ABSTRACT FROM AUTHOR]

The kinetics of the interband transitions in optically excited semiconductors is discussed and a brief historic review of this field is given. As an introductory example the free-carrier kinetics is formulated in terms of nonequilibrium Green functions, resulting in the semiconductor optical Bloch equations. [ABSTRACT FROM AUTHOR]

The theory of time-dependent transport phenomena in mesoscopic structures is formulated. Results are presented for a periodically modulated and a fluctuating resonant level model. A theory of noise is also developed. [ABSTRACT FROM AUTHOR]

Stationary transport properties of tunneling structures such as doublebarrier semiconductor heterostructures, superlattices, metallic nanowires, and Coulomb blockade structures are treated as examples for quantum transport through mesoscopic systems [ABSTRACT FROM AUTHOR]

The optical absorption of intense THz radiation in a two-band semiconductor is calculated. For this end the two-time interband susceptibility is expressed in terms of nonequilibrium Green functions. A number of special cases are calculated explicitly. The approach is generalized to include excitonic effects. Finally the theoretical predictions are compared to measured spectra. [ABSTRACT FROM AUTHOR]

As the device size shrinks, and the operating voltage is necessarily bounded from below, the electric fields inside the device must grow. In this chapter, we will address high-field transport phenomena in a systematic manner, and as a first step we study the general properties of free field-dependent Green functions which form the basic building blocks of the subsequent theory. In order to gain insight of how the general approach works, we next study a specific model of dynamical disorder, for which an analytic and exact theory can be developed. Finally, we give an extensive treatment of high-field transport in semiconductors, focusing in particular to the modifications one must make to the semiclassical Boltzmann equation. [ABSTRACT FROM AUTHOR]

The quantum transport equation in the linear limit is derived. For the particularly transparent case of electron-elastic impurity scattering contact is made with the Kubo formalism. Finally the weak localization corrections to the electrical conductivity are derived from the linearized quantum transport equation. [ABSTRACT FROM AUTHOR]

The quantum kinetic equation is in the slowly-varying center-of-mass coordinate approximation expressed in terms of the Wigner function. The collision integral is simplified by means of the generalized Kadanoff—Baym ansatz formulated in a gauge invariant way which respects causality. [ABSTRACT FROM AUTHOR]

A formulation of the quantum kinetic equation is given which is independent of the particular choice of the electrodynamic scalar and vector potentials. Because the evaluation of the collision term also requires the knowledge of the spectral Green functions, the gauge invariant equation for the retarded Green function is given as well. [ABSTRACT FROM AUTHOR]

We demonstrate how one recovers the Boltzmann equation from the quantum kinetic equation by a gradient expansion which holds if the variation of the center-of-mass coordinates is slow compared to that of the relative coordinates. Furthermore, it is necessary for this recovery that the spectral functions are sufficiently sharp. [ABSTRACT FROM AUTHOR]

The basic quantum kinetic equation which describes the time evolution of the particle propagator (or, the lesser Green function) G> is discussed in the formulations due to Kadanoff-Baym and due to Keldysh. [ABSTRACT FROM AUTHOR]

We introduce the concept of nonequilibrium Green functions which are ordered on a time contour - also called Keldysh contour - running from the remote past where the system was in equilibrium to the highest relevant time and back to the remote past. The resulting four Green functions are shown to be interrelated, but two of them, e.g., a spectral Green function and a kinetic Green function contain in nonequilibrium separate information in sharp contrast to the equilibrium situation. Using analytic continuation useful relations for products of Green functions are derived. [ABSTRACT FROM AUTHOR]

The second quantization for many-body systems is introduced. Within this formalism an elementary derivation of a non-Markovian quantum kinetic equation is given for the reduced density matrix. Next we review the equilibrium Green functions, including the dissipation-fluctuation theorem, the self-energy concept, and the perturbation expansion. [ABSTRACT FROM AUTHOR]

Various concepts for the numerical solution of the semiclassical Boltzmann equation are discussed, including an illustration of the use of a linearized Boltzmann equation and its eigenfunction expansion for a 2D electron gas. The numerical results for the linearized Boltzmann equation are compared with those of an ensemble Monte Carlo simulation of the Master equation. Finally the Boltzmann equation together with the Poisson equation is solved self-consistently for a spatially inhomogeneous electron gas in the relaxation time approximation. [ABSTRACT FROM AUTHOR]

We review some of the general properties of the semiclassical Boltzmann equation - not necessarily restricting ourselves to the dilute electron gas - paying special attention to its irreversible properties. [ABSTRACT FROM AUTHOR]