Optimizing the catching of atoms or molecules in two-dimensional traps

Single-photon cooling is a recently introduced method to cool atoms and molecules for which standard methods might not be applicable. We numerically examine this method in a two-dimensional wedge trap as well as in a two-dimensional harmonic trap. An element of the method is an optical dipole box trapping atoms irreversibly. We show that the cooling efficiency of the single-photon method can be improved by optimizing the trajectory of this optical dipole box.Comment: 8 pages, 11 figures, improved version with corrected typos et

Robust quantum control by shaped pulse

Considering the problem of the control of a two-state quantum system by an external field, we establish a general and versatile method that allows the derivation of smooth pulses, suitable for ultrafast applications, that feature the properties of high-fidelity, robustness, and low area. Such shaped pulses can be viewed as a single-shot generalization of the composite pulse technique with a time-dependent phase

Small World Graphs by the iterated "My Friends are Your Friends'' Principle

We study graphs obtained by successive creation and destruction of edges into small neighborhoods of the vertices. Starting with a circle graph of large diameter we obtain small world graphs with logarithmic diameter, high clustering coefficients and a fat tail distribution for the degree. Only local edge formation processes are involved and no preferential attachment was used. Furthermore we found an interesting phase transition with respect to the initial conditions.Comment: Latex, 12 pages with 10 figure