CiteULike: Tag atomic-evolution

Inversionless gain versus efficient gain: The autoionizing states configuration

Bruno Zambon — 2006-10-26T16:52:41-00:00

Physical Review A (Atomic, Molecular, and Optical Physics), Vol. 58, No. 1. (1998), pp. 690-699.

The absorption and stimulated emission of coherent electromagnetic radiation tuned close to an autoionizing state is investigated with the aim of clarifying some of the aspects behind the proposals of inversionless gain involving such atomic configurations. This is carried out within the framework of individual atomic evolution rather than by the use of density matrix equations, thus providing better insight into the fundamental processes of absorption and emission. In particular, we find that stimulated emission does not overcome absorption in spite of quantum interference of the Fano type being present. It is also shown that gain, in this configuration, although it can take place without population inversion between the involved levels, requires in any case a strong departure from thermal equilibrium conditions. Thereby a strong pumping mechanism, or equivalently a strong excitation power, is needed to reach the lasing threshold. This raises some questions on the relevance of the population inversion indicator of efficient gain implicitly assumed in similar configurations and in many related works.

Monte Carlo simulation of the atomic master equation for spontaneous emission

R Dum — 2006-10-26T18:52:06-00:00

Physical Review A, Vol. 45, No. 7. (1 April 1992), 4879.

A Monte Carlo simulation of the atomic master equation for spontaneous emission in terms of atomic wave functions is developed. Realizations of the time evolution of atomic wave functions are constructed that correspond to an ensemble of atoms driven by laser light undergoing a sequence of spontaneous emissions. The atomic decay times are drawn according to the photon count distribution of the driven atom. Each quantum jump of the atomic electron projects the atomic wave function to the ground state of the atom. Our theory is based on a stochastic interpretation and generalization of Mollowâs pure-state analysis of resonant light scattering; and the Srinivas-Davies theory of continuous measurements in photodetection. An extension of the theory to include mechanical light effects and a generalization to atomic systems with Zeeman substructure are given. We illustrate the method by simulating the solutions of the optical Bloch equations for two-level systems; and laser cooling of a two-level atom in an ion trap where the center-of-mass motion of the atom is described quantum mechanically.

Wave-function approach to dissipative processes in quantum optics

Jean Dalibard — 2006-10-26T18:48:18-00:00

Physical Review Letters, Vol. 68, No. 5. (3 February 1992), 580.

A novel treatment of dissipation of energy from a ââsmallââ quantum system to a reservoir is presented. We replace the usual master equation for the small-system density matrix by a wave-function evolution including a stochastic element. This wave-function approach provides new insight and it allows calculations on problems which would otherwise be exceedingly complicated. The approach is applied here to a two- or three-level atom coupled to a laser field and to the vacuum modes of the quantized electromagnetic field.