A modern review of the two-level approximation
Abstract
The paradigm of the two-level atom is revisited and its perturbative analysis is discussed in view of the principle of duality in perturbation theory. The models we consider are a two-level atom and an ensemble of two-level atoms both interacting with a single radiation mode. The aim is to see how the latter can be actually used as an amplifier of quantum fluctuations to the classical level through the thermodynamic limit of a very large ensemble of two-level atoms [M. Frasca, Phys. Lett. A {\bf 283}, 271 (2001)] and how can remove Schr\"odinger cat states. The thermodynamic limit can be very effective for producing both classical states and decoherence on a quantum system that evolves without dissipation. Decoherence without dissipation is indeed an effect of a single two-level atom interacting with an ensemble of two-level atoms, a situation that proves to be useful to understand recent experiments on nanoscale devices showing unexpected disappearance of quantum coherence at very low temperatures.
Cite
@article{arxiv.quant-ph/0209056,
title = {A modern review of the two-level approximation},
author = {Marco Frasca},
journal= {arXiv preprint arXiv:quant-ph/0209056},
year = {2007}
}
Comments
20 pages, no figures. Revised version accepted for publication in Annals of Physics