735 research outputs found
Reply to "Comment on 'Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate'"
In the Comment by M. Mackie \textit{et al.} [arXiv: physics/0212111 v.4], the
authors suggest that the molecular conversion efficiency in atom-molecule
STIRAP can be improved by lowering the initial atomic density, which in turn
requires longer pulse durations to maintain adiabaticity. Apart from the fact
that the mean-field approximation becomes questionable at low densities, we
point out that a low-density strategy with longer pulses has several problems.
It generally requires higher pulse energies, and increases radiative losses. We
also show that even within the approximations used in the Comment, their
example leads to no efficiency improvement compared to our high-density case.
In a more careful analysis including radiative losses neglected in the Comment,
the proposed strategy gives almost no conversion owing to the longer pulse
durations required.Comment: Accepted for publication in Phys. Rev.
Bragg spectroscopy of a superfluid Bose-Hubbard gas
Bragg spectroscopy is used to measure excitations of a trapped,
quantum-degenerate gas of 87Rb atoms in a 3-dimensional optical lattice. The
measurements are carried out over a range of optical lattice depths in the
superfluid phase of the Bose-Hubbard model. For fixed wavevector, the resonant
frequency of the excitation is found to decrease with increasing lattice depth.
A numerical calculation of the resonant frequencies based on Bogoliubov theory
shows a less steep rate of decrease than the measurements.Comment: 11 pages, 4 figure
Linking Ultracold Polar Molecules
We predict that pairs of polar molecules can be weakly bound together in an
ultracold environment, provided that a dc electric field is present. The field
that links the molecules together also strongly influences the basic properties
of the resulting dimer, such as its binding energy and predissociation
lifetime. Because of their long-range character these dimers will be useful in
disentangling cold collision dynamics of polar molecules. As an example, we
estimate the microwave photoassociation yield for OH-OH cold collisions.Comment: 4 pages 2 figure
Sounding Vessel Position From Adjustment by Variation of Parameters
For hydrographic surveys conducted by the U.S. Naval Oceanographic Office, the position of a sounding vessel is determined by applying the method of adjustment by variation of parameters. Three types of navigational aids are used: ranging, azimuthal, and hyperbolic. Given data from any combination of at least two navigational aids, a fix may be obtained using an iterative method, which applies successive adjustments to an approximate location and forces it to converge to the most probable position. The magnitude and direction of each adjustment is determined from a least squares solution that minimizes the residual differences between actual navigational observations and imaginary observations calculated as if the ship were at the approximate location
Multi-channel scattering and Feshbach resonances: Effective theory, phenomenology, and many-body effects
A low energy effective theory based on a microscopic multi-channel
description of the atom-atom interaction is derived for the scattering of
alkali atoms in different hyperfine states. This theory describes all
scattering properties, including medium effects, in terms of the singlet and
triplet scattering lengths and the range of the atom-atom potential and
provides a link between a microscopic description of Feshbach scattering and
more phenomenological approaches. It permits the calculation of medium effects
on the resonance coming from the occupation of closed channel states. The
examination of such effects are demonstrated to be of particular relevance to
an experimentally important Feshbach resonance for K atoms. We analyze a
recent rethermalization rate experiment on K and demonstrate that a
measurement of the temperature dependence of this rate can determine the
magnetic moment of the Feshbach molecule. Finally, the energy dependence of the
Feshbach interaction is shown to introduce a negative effective range inversely
proportional to the width of the resonance. Since our theory is based on a
microscopic multi-channel picture, it allows the explicit calculation of
corrections to commonly used approximations such as the neglect of the
effective range and the treatment of the Feshbach molecule as a point boson.Comment: 10 pages, 5 figures. Typos corrected. Accepted for PR
Resposta das videiras a diferentes modos de distribuição de composto orgânico no solo.
O trabalho objetivou avaliar o estado nutricional, a produção e a composição do mosto de uvas em videiras submetidas a diferentes modos de distribuição de composto orgânico no solo. O experimento foi conduzido em um vinhedo da cv. Cabernet Sauvignon, com plantas enxertadas sobre o porta-enxerto 'Paulsen 1103' em um solo Neossolo Litólico, em Bento Gonçalves (RS). Em agosto de 2006, foram implantados os tratamentos (T1) testemunha; (T2) aplicação de composto orgânico na superfície do solo sempre no mesmo lado da linha de plantio; (T3) aplicação de composto em lados alternados da linha de plantio ao longo dos anos; (T4) aplicação de composto em covas sempre do mesmo lado da linha de plantio, e (T5) aplicação de composto em covas em lados alternados na linha de plantio ao longo dos anos. Nas safras de 2006/2007, 2007/2008 e 2008/2009, os ramos da poda de inverno e o tecido da poda de verão foram secos e determinada a produção de matéria seca. Folhas completas foram coletadas, secas, moídas e submetidas à análise do teor total de N, P, K, Ca e Mg. Na maturação, foi contado o número de cachos e pesados, e, em seguida, bagas foram coletadas e determinados os valores de sólidos solúveis, pH, acidez titulável, ácido tartárico e málico. A distribuição de composto em covas sempre do mesmo lado da linha de plantio ou em lados alternados ao longo dos anos aumentou a quantidade de matéria seca dos ramos podados no inverno, especialmente, nas primeiras safras depois de sua aplicação. A aplicação e o modo de distribuição do composto na superfície do solo ou incorporado, anualmente no mesmo lado da linha de plantio ou alternado entre os lados ao longo dos anos, não afetaram a produção de uva, o estado nutricional e a composição do mosto, e, quando necessário, o composto orgânico deve ser aplicado na superfície do solo sem incorporação, em um mesmo lado da linha de plantio ou alternado entre os lados ao longo dos anos
Rate limit for photoassociation of a Bose-Einstein condensate
We simulate numerically the photodissociation of molecules into noncondensate
atom pairs that accompanies photoassociation of an atomic Bose-Einstein
condensate into a molecular condensate. Such rogue photodissociation sets a
limit on the achievable rate of photoassociation. Given the atom density \rho
and mass m, the limit is approximately 6\hbar\rho^{2/3}/m. At low temperatures
this is a more stringent restriction than the unitary limit of scattering
theory.Comment: 5 pgs, 18 refs., 3 figs., submitted to Phys. Rev. Let
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