Figure 1. A single-photon (indicated by a wavy line) coherent (indicated by a double electron line) radiative transition in the presence of an external field (indicated by a dashed virtual photon line), a laser scheme for a three-level atom, and systems of interest (a many-electron atom, a magnetic wiggler for a free-electron laser, and a crystal lattice).
Figure 1. A single-photon (indicated by a wavy line) coherent (indicated by a double electron line) radiative transition in the presence of an external field (indicated by a dashed virtual photon line), a laser scheme for a three-level atom, and systems of interest (a many-electron atom, a magnetic wiggler for a free-electron laser, and a crystal lattice).

Quantum-open-systems (reduced-density-matrix) approaches are developed for non-equilibrium (possibly coherent) electromagnetic interactions in quantized electronic systems, in the presence of environmental relaxation and decoherence phenomena. The electronic systems of interest include ensembles of many-electron atoms, energetic electron beams in crystals and in electric and magnetic fields, and semiconductor materials (ideal crystals and heterostructures). Linear and non-linear optical phenomena are investigated within the frameworks of semi-classical and fully-quantum mechanical (QED) formulations.

Coherent electromagnetic interactions play an important role in optical communication (including light propagation, delay, and storage), coherent quantum control of reaction processes, and laser physics. Coherent interactions are most efficient when a certain resonance (or phase-matching) condition is maintained. In quantized electronic systems, coherent electromagnetic interactions can be strongly influenced by the surrounding environment of charged particles and electromagnetic fields. The electronic states, which may be single-electron or many-electron states, are modified (or renormalized) as a result of the environmental electron-electron, electron-phonon, and electron-photon interactions.

A comprehensive reduced-density-matrix description, applicable to resonant and non-resonant electromagnetic transitions of quantized electronic systems, has been under development. On a formally equal footing, coherent interactions can be treated together with environmental relaxation and decoherence phenomena. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. Non-equilibrium quantum-statistical description of coherent electronic-state kinetics and homogeneous spectral-line shapes (or laser gain profiles) are self-consistently obtained. A major challenge is the practical incorporation of a quantum-correlation hierarchy, which involves the coupling of, for example, single-particle reduced dynamics to two-particle reduced dynamics.

Quantized (or quantum-confined) electronic systems are characterized by discrete or nearly discrete energy-level structures (which correspond to bound or quasi-bound states) and by radiative transitions that give rise to line-like spectral features in absorption or emission processes. Such transitions are advantageous for the generation of coherent electromagnetic radiation and also provide the basis for the precise spectroscopic investigation of the electronic structure and optical properties of materials. A unified investigation has been carried out for radiative and dielectronic recombination of many-electron atomic systems with beam or plasma electrons. A research area of current interest involves linear and non-linear optical interactions in bulk semiconductor materials and in semiconductor heterostructures (quantum wells, wires, and dots).
Principal Investigator: Verne Jacobs