Validity Of Semiclassical Approximation Research Articles

Collapse-revival dynamics and atom-field entanglement in the nonresonant Dicke model

We consider the dynamics of atomic and field coherent states in the nonresonant Dicke model. At weak coupling an initial product state evolves into a superposition of multiple field coherent states that are correlated with the atomic configuration. This process is accompanied by the buildup and decay of atom-field entanglement and leads to the periodic collapse and revival of Rabi oscillations. We provide a perturbative derivation of the underlying dynamical mechanism that complements the rotating wave approximation at resonance. The identification of two different time scales explains how the dynamical signatures depend on the sign of detuning between the atomic and field frequency and predicts the generation of either atomic or field cat states in the two opposite cases. We finally discuss the restrictions that the buildup of atom-field entanglement during the collapse of Rabi oscillations impose on the validity of semiclassical approximations that neglect entanglement.

Scattering of light exotic atoms in excited states

The differential and total cross sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined.

Subbands in Space-Charge Layers on Narrow Gap Semiconductors: Validity of Semiclassical Approximation

A simplified approximation scheme is proposed for the calculation of subband energy levels in space-charge layers on narrow-gap semiconductors. The method consists of using the potential calculated in the classical approximation and also the WKB approximation. Its validity is demonstrated through comparison with results of more elaborate self-consistent calculations.