1,290 research outputs found
Scattering lengths of calcium and barium isotopes
We have calculated the s-wave scattering length of all the even isotopes of
calcium (Ca) and barium (Ba), in order to investigate the prospect of
Bose-Einstein condensation (BEC). For Ca we have used an accurate molecular
potential based on detailed spectroscopic data. Our calculations show that Ca
does not provide other isotopes alternative to the recently Bose condensed 40Ca
that suffers strong losses because of a very large scattering length. For Ba we
show by using a model potential that the even isotopes cover a broad range of
scattering lengths, opening the possibility of BEC for at least one of the
isotopes.Comment: 4 page
Non-exponential one-body loss in a Bose-Einstein condensate
We have studied the decay of a Bose-Einstein condensate of metastable helium
atoms in an optical dipole trap. In the regime where two- and three-body losses
can be neglected we show that the Bose-Einstein condensate and the thermal
cloud show fundamentally different decay characteristics. The total number of
atoms decays exponentially with time constant tau; however, the thermal cloud
decays exponentially with time constant (4/3)tau and the condensate decays much
faster, and non-exponentially. We show that this behaviour, which should be
present for all BECs in thermal equilibrium with a considerable thermal
fraction, is due to a transfer of atoms from the condensate to the thermal
cloud during its decay.Comment: The intuitive explanation of the atomic transfer effect has been
correcte
Ultracold mixtures of metastable He and Rb: scattering lengths from ab initio calculations and thermalization measurements
We have investigated the ultracold interspecies scattering properties of
metastable triplet He and Rb. We performed state-of-the-art ab initio
calculations of the relevant interaction potential, and measured the
interspecies elastic cross section for an ultracold mixture of metastable
triplet He and Rb in a quadrupole magnetic trap at a temperature of
0.5 mK. Our combined theoretical and experimental study gives an interspecies
scattering length , which prior to this work was
unknown. More general, our work shows the possibility of obtaining accurate
scattering lengths using ab initio calculations for a system containing a
heavy, many-electron atom, such as Rb.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.
Metastable Feshbach Molecules in High Rotational States
We experimentally demonstrate Cs2 Feshbach molecules well above the
dissociation threshold, which are stable against spontaneous decay on the
timescale of one second. An optically trapped sample of ultracold dimers is
prepared in an l-wave state and magnetically tuned into a region with negative
binding energy. The metastable character of these molecules arises from the
large centrifugal barrier in combination with negligible coupling to states
with low rotational angular momentum. A sharp onset of dissociation with
increasing magnetic field is mediated by a crossing with a g-wave dimer state
and facilitates dissociation on demand with a well defined energy.Comment: 4 pages, 5 figure
Faster Algorithms for Weighted Recursive State Machines
Pushdown systems (PDSs) and recursive state machines (RSMs), which are
linearly equivalent, are standard models for interprocedural analysis. Yet RSMs
are more convenient as they (a) explicitly model function calls and returns,
and (b) specify many natural parameters for algorithmic analysis, e.g., the
number of entries and exits. We consider a general framework where RSM
transitions are labeled from a semiring and path properties are algebraic with
semiring operations, which can model, e.g., interprocedural reachability and
dataflow analysis problems.
Our main contributions are new algorithms for several fundamental problems.
As compared to a direct translation of RSMs to PDSs and the best-known existing
bounds of PDSs, our analysis algorithm improves the complexity for
finite-height semirings (that subsumes reachability and standard dataflow
properties). We further consider the problem of extracting distance values from
the representation structures computed by our algorithm, and give efficient
algorithms that distinguish the complexity of a one-time preprocessing from the
complexity of each individual query. Another advantage of our algorithm is that
our improvements carry over to the concurrent setting, where we improve the
best-known complexity for the context-bounded analysis of concurrent RSMs.
Finally, we provide a prototype implementation that gives a significant
speed-up on several benchmarks from the SLAM/SDV project
Magnetically Controlled Exchange Process in an Ultracold Atom-Dimer Mixture
We report on the observation of an elementary exchange process in an
optically trapped ultracold sample of atoms and Feshbach molecules. We can
magnetically control the energetic nature of the process and tune it from
endoergic to exoergic, enabling the observation of a pronounced threshold
behavior. In contrast to relaxation to more deeply bound molecular states, the
exchange process does not lead to trap loss. We find excellent agreement
between our experimental observations and calculations based on the solutions
of three-body Schr\"odinger equation in the adiabatic hyperspherical
representation. The high efficiency of the exchange process is explained by the
halo character of both the initial and final molecular states.Comment: 4 pages, 4 figure
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