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We show that the initial dynamics of resonantly-excited excitons in quantum wells is controlled by several processes such as radiative recombination, spin relaxation of excitons, electrons and holes, and scattering between different in-plane momentum states of excitons. We present a unifïed analysis of the results, which provides quantitative information about these important rates, and a good physical understanding of the initial dynamics of nonequilibrium excitons. In particular, we show that the enhanced radiative recombination rate of excitons makes an important contribution to the early decay of the photoluminescence.

A precise time-dependent control of a quantum system relies on an accurate account of the quantum interference among the system, the control, and the environment. A diagrammatic technique has been recently developed to precisely calculate this quantum correlation for a fast multimode coherent photon control against slow relaxation, valid for both Markovian and non-Markovian systems. We review this formalism in comparison with the existing approximate theories and extend it to cases with controls by photon state other than the coherent state.

We review the investigation of the hole-assisted dynamical nuclear spin polarization mechanism in a singly charged InAs quantum dot. Using coherent dark state spectroscopy, we measure the locking of the Overhauser field to a value determined only by the laser frequencies. Importantly, we review data that the locking effect can suppress nuclear spin fluctuations. We determine the onset time of the nuclear spin narrowing effect and its persistence absent laser interactions by directly measuring the enhancement of the electron spin coherence. This nuclear field locking effect can be explained in terms of an anisotropic hyperfine coupling between the hole spin and the nuclear spins.

For non-phonon interaction mechanisms which span a frequency range comparable to the Fermi energy, solution of the Eliashberg equation must cover both a range of frequencies and a range of momentum values. Kirzhnits, Maksimov, and Khomskii (KMK) have derived an intergral equation for the superconducting transition where frequency is eliminated in favor of the momentum. We have found a systematic correction to the KMK equation and investigated the effect onTcfor model interactions.