2,117 research outputs found
Effect of Magnetization Inhomogeneity on Magnetic Microtraps for Atoms
We report on the origin of fragmentation of ultracold atoms observed on a
permanent magnetic film atom chip. A novel technique is used to characterize
small spatial variations of the magnetic field near the film surface using
radio frequency spectroscopy of the trapped atoms. Direct observations indicate
the fragmentation is due to a corrugation of the magnetic potential caused by
long range inhomogeneity in the film magnetization. A model which takes into
account two-dimensional variations of the film magnetization is consistent with
the observations.Comment: 4 pages, 4 figure
Precision measurements of s-wave scattering lengths in a two-component Bose-Einstein condensate
We use collective oscillations of a two-component Bose-Einstein condensate
(2CBEC) of \Rb atoms prepared in the internal states and for the precision measurement of
the interspecies scattering length with a relative uncertainty of
. We show that in a cigar-shaped trap the three-dimensional
(3D) dynamics of a component with a small relative population can be
conveniently described by a one-dimensional (1D) Schr\"{o}dinger equation for
an effective harmonic oscillator. The frequency of the collective oscillations
is defined by the axial trap frequency and the ratio , where
is the intra-species scattering length of a highly populated component
1, and is largely decoupled from the scattering length , the total atom
number and loss terms. By fitting numerical simulations of the coupled
Gross-Pitaevskii equations to the recorded temporal evolution of the axial
width we obtain the value , where is the Bohr
radius. Our reported value is in a reasonable agreement with the theoretical
prediction but deviates significantly from the
previously measured value \cite{Mertes07} which is commonly
used in the characterisation of spin dynamics in degenerate \Rb atoms. Using
Ramsey interferometry of the 2CBEC we measure the scattering length
which also deviates from the previously reported value
\cite{Mertes07}. We characterise two-body losses for the
component 2 and obtain the loss coefficients
and
.Comment: 11 pages, 8 figure
Incoherent pion photoproduction on the deuteron in the first resonance region
Incoherent pion photoproduction on the deuteron is studied in the first
resonance region. The unpolarized cross section, the beam asymmetry, and the
vector and tensor target asymmetries are calculated in the framework of a
diagrammatic approach. Pole diagrams and one-loop diagrams with scattering
in the final state are taken into account. An elementary operator for pion
photoproduction on the nucleon is taken in various on-shell forms and
calculated using the SAID and MAID multipole analyses. Model dependence of the
obtained results is discussed in some detail. A comparison with predictions of
other works is given. Although a reasonable description of many available
experimental data on the unpolarized total and differential cross sections and
photon asymmetry has been achieved, in some cases a significant disagreement
between the theory and experiment has been found. Invoking known information on
the reactions and we predict the total
photoabsorption cross section for deuterium. We find that our values strongly
overestimate experimental data in the vicinity of the peak.Comment: 22 pages, 23 figure
Asymmetric double-well potential for single atom interferometry
We consider the evolution of a single-atom wavefunction in a time-dependent
double-well interferometer in the presence of a spatially asymmetric potential.
We examine a case where a single trapping potential is split into an asymmetric
double well and then recombined again. The interferometer involves a
measurement of the first excited state population as a sensitive measure of the
asymmetric potential. Based on a two-mode approximation a Bloch vector model
provides a simple and satisfactory description of the dynamical evolution. We
discuss the roles of adiabaticity and asymmetry in the double-well
interferometer. The Bloch model allows us to account for the effects of
asymmetry on the excited state population throughout the interferometric
process and to choose the appropriate splitting, holding and recombination
periods in order to maximize the output signal. We also compare the outcomes of
the Bloch vector model with the results of numerical simulations of the
multi-state time-dependent Schroedinger equation.Comment: 9 pages, 6 figure
Semiclassical correlators of three states with large S^5 charges in string theory in AdS_5 x S^5
We consider semiclassical computation of 3-point correlation functions of
(BPS or non-BPS) string states represented by vertex operators carrying large
charges in S5. We argue that the AdS5 part of the construction of relevant
semiclassical solution involves the two basic ingredients: (i) configuration of
three glued geodesics in AdS2 suggested by Klose and McLoughlin in
arXiv:1106.0495 and (ii) a particular Schwarz-Christoffel map of the 3-geodesic
solution in cylindrical (tau, sigma) domain into the complex plane with three
marked points. This map is constructed using the expression for the AdS2 string
stress tensor which is uniquely determined by the 3 scaling dimensions as noted
by Janik and Wereszczynski in arXiv:1109.6262 (our solution, however, is
different from theirs). We also find the S5 part of the solution and thus the
full expression for the semiclassical part of the 3-point correlator for
several examples: extremal and non-extremal correlators of BPS states and a
particular correlator of "small" circular spinning strings in S3 part of S5. We
demonstrate that for the BPS correlators the results agree with the large
charge limit of the corresponding supergravity and free gauge theory
expressions.Comment: 43 pages, 4 figures; v2: minor corrections; v3: comments added at the
end of section 3 and in section 5; v4: minor corrections; v5: discussion in
subsection 3.3 correcte
Mean-field dynamics of two-mode Bose-Einstein condensates in highly anisotropic potentials: Interference, dimensionality, and entanglement
We study the mean-field dynamics and the reduced-dimension character of
two-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means
of perturbative techniques, we show that the tightly confined (transverse)
degrees of freedom can be decoupled from the dynamical equations at the expense
of introducing additional effective three-body, attractive, intra- and
inter-mode interactions into the dynamics of the loosely confined
(longitudinal) degrees of freedom. These effective interactions are mediated by
changes in the transverse wave function. The perturbation theory is valid as
long as the nonlinear scattering energy is small compared to the transverse
energy scales. This approach leads to reduced-dimension mean-field equations
that optimally describe the evolution of a two-mode condensate in general
quasi-1D and quasi-2D geometries. We use this model to investigate the relative
phase and density dynamics of a two-mode, cigar-shaped Rb BEC. We study
the relative-phase dynamics in the context of a nonlinear Ramsey interferometry
scheme, which has recently been proposed as a novel platform for high-precision
interferometry. Numerical integration of the coupled, time-dependent,
three-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers
shows that this model gives a considerably more refined analytical account of
the mean-field evolution than an idealized quasi-1D description.Comment: 35 pages, 10 figures. Current version is as publishe
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