ICAM Theme

Professor Ilias Perakis

Vanderbilt University

Department of Physics & Astronomy

Station B, Box 1807

Nashville, TN 37238

(615) 322-2828

ilias@lefteris.phy.vanderbilt.edu

During the past decade, coherent ultrafast nonlinear optical spectroscopy has become a sensitive experimental tool for studying many--body correlations. The two--level system models, often used to interpret such experiments in atomic systems, cannot explain qualitative features in the nonlinear dynamical response of semiconductor quantum wells. The interpretation of such features retains the challenge of the many--body problem, i.e., how to explain and predict properties of systems possessing many degrees of freedom in terms of their fundamental interactions.

Given the complexity of describing the femtosecond time evolution of such systems, arising from interactions among, e.g., optically-excited and Fermi sea carriers, a hierarchy of successive approximations has been formulated. To lowest order, this corresponds to the time-dependent Hartree-Fock approximation (Semiconductor Bloch Equations), which treat the interactions at the mean--field level. Pronounced features in the amplitude and phase dynamics of the nonlinear polarizations have been attributed to correlation effects beyond this mean field level. These cannot be treated within the usual effective lifetime and quasi--equilibrium (Markovian) approximations. During the past few years, there is an ongoing theoretical effort aimed at describing phenomena at the femtosecond time scale that arise from non--perturbative many--body effects.

The role of non-equilibrium correlations in the femtosecond time evolution of the coherent nonlinear optical spectra presents a many--body problem at the frontier of Condensed Matter Physics. Furthermore, the importance of analogous correlations in biological, molecular, and atomic systems make this topic truly interdisciplinary and a suitable theme for ICAM.