1,538 research outputs found
Molecular Feshbach dissociation as a source for motionally entangled atoms
We describe the dissociation of a diatomic Feshbach molecule due to a
time-varying external magnetic field in a realistic trap and guide setting. An
analytic expression for the asymptotic state of the two ultracold atoms is
derived, which can serve as a basis for the analysis of dissociation protocols
to generate motionally entangled states. For instance, the gradual dissociation
by sequences of magnetic field pulses may delocalize the atoms into
macroscopically distinct wave packets, whose motional entanglement can be
addressed interferometrically. The established relation between the applied
magnetic field pulse and the generated dissociation state reveals that
square-shaped magnetic field pulses minimize the momentum spread of the atoms.
This is required to control the detrimental influence of dispersion in a
recently proposed experiment to perform a Bell test in the motion of the two
atoms [C. Gneiting and K. Hornberger, Phys. Rev. Lett. 101, 260503 (2008)].Comment: 12 pages, 3 figures; corresponds to published versio
Ensemble model output statistics for wind vectors
A bivariate ensemble model output statistics (EMOS) technique for the
postprocessing of ensemble forecasts of two-dimensional wind vectors is
proposed, where the postprocessed probabilistic forecast takes the form of a
bivariate normal probability density function. The postprocessed means and
variances of the wind vector components are linearly bias-corrected versions of
the ensemble means and ensemble variances, respectively, and the conditional
correlation between the wind components is represented by a trigonometric
function of the ensemble mean wind direction. In a case study on 48-hour
forecasts of wind vectors over the North American Pacific Northwest with the
University of Washington Mesoscale Ensemble, the bivariate EMOS density
forecasts were calibrated and sharp, and showed considerable improvement over
the raw ensemble and reference forecasts, including ensemble copula coupling
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