246 research outputs found
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
Asymmetric scattering by non-hermitian potentials
The scattering of quantum particles by non-hermitian (generally nonlocal)
potentials in one dimension may result in asymmetric transmission and/or
reflection from left and right incidence. Eight generalized symmetries based on
the discrete Klein's four-group (formed by parity, time reversal, their
product, and unity) are used together with generalized unitarity relations to
determine the possible and/or forbidden scattering asymmetries. Six basic
device types are identified when the scattering coefficients (squared moduli of
scattering amplitudes) adopt zero/one values, and transmission and/or
reflection are asymmetric. They can pictorially be described as a one-way
mirror, a one-way barrier (a Maxwell pressure demon), one-way (transmission or
reflection) filters, a mirror with unidirectional transmission, and a
transparent, one-way reflector. We design potentials for these devices and also
demonstrate that the behavior of the scattering coefficients can be extended to
a broad range of incident momenta
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
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