1,310 research outputs found
Manipulation of a Bose-Einstein condensate by a time-averaged orbiting potential using phase jumps of the rotating field
We report on the manipulation of the center-of-mass motion (`sloshing') of a
Bose Einstein condensate in a time-averaged orbiting potential (TOP) trap. We
start with a condensate at rest in the center of a static trapping potential.
When suddenly replacing the static trap with a TOP trap centered about the same
position, the condensate starts to slosh with an amplitude much larger than the
TOP micromotion. We show, both theoretically and experimentally, that the
direction of sloshing is related to the initial phase of the rotating magnetic
field of the TOP. We show further that the sloshing can be quenched by applying
a carefully timed and sized jump in the phase of the rotating field.Comment: 11 pages, 9 figure
Controlling integrability in a quasi-1D atom-dimer mixture
We analytically study the atom-dimer scattering problem in the
near-integrable limit when the oscillator length l_0 of the transverse
confinement is smaller than the dimer size, ~l_0^2/|a|, where a<0 is the
interatomic scattering length. The leading contributions to the atom-diatom
reflection and break-up probabilities are proportional to a^6 in the bosonic
case and to a^8 for the up-(up-down) scattering in a two-component fermionic
mixture. We show that by tuning a and l_0 one can control the "degree of
integrability" in a quasi-1D atom-dimer mixture in an extremely wide range
leaving thermodynamic quantities unchanged. We find that the relaxation to
deeply bound states in the fermionic (bosonic) case is slower (faster) than
transitions between different Bethe ansatz states. We propose a realistic
experiment for detailed studies of the crossover from integrable to
nonintegrable dynamics.Comment: 12 pages, 1 figur
Atom-dimer scattering and long-lived trimers in fermionic mixtures
We consider a heteronuclear fermionic mixture on the molecular side of an
interspecies Feshbach resonance and discuss atom-dimer scattering properties in
uniform space and in the presence of an external confining potential,
restricting the system to a quasi-2D geometry. We find that there is a peculiar
atom-dimer p-wave resonance which can be tuned by changing the frequency of the
confinement. Our results have implications for the ongoing experiments on
Lithium-Potassium mixtures, where this mechanism allows for switching the
p-wave interaction between a K atom and Li-K dimer from attractive to
repulsive, and forming a weakly bound trimer with unit angular momentum. We
show that such trimers are long-lived and the atom-dimer resonance does not
enhance inelastic relaxation in the mixture, making it an outstanding candidate
for studies of p-wave resonance effects in a many-body system.Comment: 4 pages, 2 figures, published versio
Laser cooling of new atomic and molecular species with ultrafast pulses
We propose a new laser cooling method for atomic species whose level
structure makes traditional laser cooling difficult. For instance, laser
cooling of hydrogen requires single-frequency vacuum-ultraviolet light, while
multielectron atoms need single-frequency light at many widely separated
frequencies. These restrictions can be eased by laser cooling on two-photon
transitions with ultrafast pulse trains. Laser cooling of hydrogen,
antihydrogen, and many other species appears feasible, and extension of the
technique to molecules may be possible.Comment: revision of quant-ph/0306099, submitted to PR
Asymptotic Bound-state Model for Feshbach Resonances
We present an Asymptotic Bound-state Model which can be used to accurately
describe all Feshbach resonance positions and widths in a two-body system. With
this model we determine the coupled bound states of a particular two-body
system. The model is based on analytic properties of the two-body Hamiltonian,
and on asymptotic properties of uncoupled bound states in the interaction
potentials. In its most simple version, the only necessary parameters are the
least bound state energies and actual potentials are not used. The complexity
of the model can be stepwise increased by introducing threshold effects,
multiple vibrational levels and additional potential parameters. The model is
extensively tested on the 6Li-40K system and additional calculations on the
40K-87Rb system are presented.Comment: 13 pages, 8 figure
Evaporation limited loading of an atom trap
Recently, we have experimentally demonstrated a continuous loading mechanism
for an optical dipole trap from a guided atomic beam [1]. The observed
evolution of the number of atoms and temperature in the trap are consequences
of the unusual trap geometry. In the present paper, we develop a model based on
a set of rate equations to describe the loading dynamics of such a mechanism.
We consider the collision statistics in the non-uniform trap potential that
leads to twodimensional evaporation. The comparison between the resulting
computations and experimental data allows to identify the dominant loss process
and suggests ways to enhance the achievable steady-state atom number.
Concerning subsequent evaporative cooling, we find that the possibility of
controlling axial and radial confinement independently allows faster
evaporation ramps compared to single beam optical dipole traps.Comment: 10 pages, 7 figure
PERFEX: Classifier Performance Explanations for Trustworthy AI Systems
Explainability of a classification model is crucial when deployed in
real-world decision support systems. Explanations make predictions actionable
to the user and should inform about the capabilities and limitations of the
system. Existing explanation methods, however, typically only provide
explanations for individual predictions. Information about conditions under
which the classifier is able to support the decision maker is not available,
while for instance information about when the system is not able to
differentiate classes can be very helpful. In the development phase it can
support the search for new features or combining models, and in the operational
phase it supports decision makers in deciding e.g. not to use the system. This
paper presents a method to explain the qualities of a trained base classifier,
called PERFormance EXplainer (PERFEX). Our method consists of a meta tree
learning algorithm that is able to predict and explain under which conditions
the base classifier has a high or low error or any other classification
performance metric. We evaluate PERFEX using several classifiers and datasets,
including a case study with urban mobility data. It turns out that PERFEX
typically has high meta prediction performance even if the base classifier is
hardly able to differentiate classes, while giving compact performance
explanations
- …