320 research outputs found
Damping and frequency shift in the oscillations of two colliding Bose-Einstein condensates
We have investigated the center-of-mass oscillations of a Rb87 Bose-Einstein
condensate in an elongated magneto-static trap. We start from a trapped
condensate and we transfer part of the atoms to another trapped level, by
applying a radio-frequency pulse. The new condensate is produced far from its
equilibrium position in the magnetic potential, and periodically collides with
the parent condensate. We discuss how both the damping and the frequency shift
of the oscillations are affected by the mutual interaction between the two
condensates, in a wide range of trapping frequencies. The experimental data are
compared with the prediction of a mean-field model.Comment: 5 RevTex pages, 7 eps figure
Spatial interference of coherent atomic waves by manipulation of the internal quantum state
A trapped 87Rb Bose-Einstein condensate is initially put into a superposition
of two internal states. Under the effect of gravity and by means of a second
transition, we prepare two vertically displaced condensates in the same
internal state. These constitute two coherent sources of matter waves with
adjustable spatial separation. Fringe patterns, observed after free expansion,
are associated with the interplay between internal and external degrees of
freedom and substantially agree with those for a double slit experiment
Collective excitations of a trapped Bose-Einstein condensate in the presence of a 1D optical lattice
We study low-lying collective modes of a horizontally elongated 87Rb
condensate produced in a 3D magnetic harmonic trap with the addition of a 1D
periodic potential which is provided by a laser standing-wave along the
horizontal axis. While the transverse breathing mode results unperturbed,
quadrupole and dipole oscillations along the optical lattice are strongly
modified. Precise measurements of the collective mode frequencies at different
height of the optical barriers provide a stringent test of the theoretical
model recently introduced [M.Kraemer et al. Phys. Rev. Lett. 88 180404 (2002)].Comment: 4 pages, 4 figure
Quasi 2D Bose-Einstein condensation in an optical lattice
We study the phase transition of a gas of Rb atoms to quantum degeneracy in
the combined potential of a harmonically confining magnetic trap and the
periodic potential of an optical lattice. For high optical lattice potentials
we observe a significant change in the temperature dependency of the population
of the ground state of the system. The experimental results are explained by
the subsequent formation of quasi 2D condensates in the single lattice sites.Comment: 7 pages (including 3 figures
Dynamics of two colliding Bose-Einstein condensates in an elongated magneto-static trap
We study the dynamics of two interacting Bose-Einstein condensates, by
numerically solving two coupled Gross-Pitaevskii equations at zero temperature.
We consider the case of a sudden transfer of atoms between two trapped states
with different magnetic moments: the two condensates are initially created with
the same density profile, but are trapped into different magnetic potentials,
whose minima are vertically displaced by a distance much larger than the
initial size of both condensates. Then the two condensates begin to perform
collective oscillations, undergoing a complex evolution, characterized by
collisions between the two condensates. We investigate the effects of their
mutual interaction on the center-of-mass oscillations and on the time evolution
of the aspect ratios. Our theoretical analysis provides a useful insight into
the recent experimental observations by Maddaloni et al., cond-mat/0003402.Comment: 8 pages, 7 figures, RevTe
Earthquake induced floor accelerations on a high-rise building: Scale model tests on a shaking table
The paper discusses results of shaking table tests on an in-scale high-rise building model. The purpose was to calibrate a dynamic numerical model for multi-hazard analyses to investigate the effects of floor acceleration. Accelerations, because of vibration of non-structural elements, affect both the comfort and safety of people. The research investigates the acceleration effects of both seismic and wind forces on an aeroelastic in-scale model of a multi-story building. The paper discusses the first phase of experiments and gives results of floor accelerations induced by several different base seismic impulses. Structural analyses were first performed on the full-scale prototype to take soil-structure interaction into account. Subsequently the scale model was designed through aeroelastic scale laws. Shaking table experiments were then carried out under different base accelerations. The response of the model and, in particular, amplification of effects from base to top are discussed
Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF:Er
We present a detection scheme to search for QCD axion dark matter, that is
based on a direct interaction between axions and electrons explicitly predicted
by DFSZ axion models. The local axion dark matter field shall drive transitions
between Zeeman-split atomic levels separated by the axion rest mass energy . Axion-related excitations are then detected with an upconversion scheme
involving a pump laser that converts the absorbed axion energy (
hundreds of eV) to visible or infrared photons, where single photon
detection is an established technique. The proposed scheme involves rare-earth
ions doped into solid-state crystalline materials, and the optical transitions
take place between energy levels of electron configuration. Beyond
discussing theoretical aspects and requirements to achieve a cosmologically
relevant sensitivity, especially in terms of spectroscopic material properties,
we experimentally investigate backgrounds due to the pump laser at temperatures
in the range K. Our results rule out excitation of the upper Zeeman
component of the ground state by laser-related heating effects, and are of some
help in optimizing activated material parameters to suppress the
multiphonon-assisted Stokes fluorescence.Comment: 8 pages, 5 figure
Superfluid current disruption in a chain of weakly coupled Bose-Einstein Condensates
We report the experimental observation of the disruption of the superfluid
atomic current flowing through an array of weakly linked Bose-Einstein
condensates. The condensates are trapped in an optical lattice superimposed on
a harmonic magnetic potential. The dynamical response of the system to a change
of the magnetic potential minimum along the optical lattice axis goes from a
coherent oscillation (superfluid regime) to a localization of the condensates
in the harmonic trap ("classical" insulator regime). The localization occurs
when the initial displacement is larger than a critical value or, equivalently,
when the velocity of the wavepacket's center of mass is larger than a critical
velocity dependent on the tunnelling rate between adjacent sites.Comment: 8 pages, 4 figure
Gravimetry and petrophysics in the Chad basin area: determination of the basement depth and the implication for defining a scientific drilling site (ICDP-CHADRILL project)
The Chad basin is a huge intracratonic sag-basin (2.5 million km2) in the North Central Africa. In this work, we
investigated the basement depth under the Chad Lake using the inversion of gravity residual data obtained by the
regression analysis between gravity and topography data. It has been carried on with a collaboration between
the University of Trieste and the Institut de Physique du Globe, Strasbourg (IPGS) in order to contribute to the
decision of the location of a ICDP drilling site (Bol, SE Chad Lake). This project consists in a compared analysis
between gravity data with other geological/geophysical data and their interpretation in terms of tectonic features.
The main objectives of this work are: (1) estimation of the basement depth under the Chad basin through a joint
analysis and interpretation of satellite and terrestrial gravity data (GOCE, BGI) [1] with borehole data and density
values of Cameroon-Chadian rock samples. (2) Estimation and interpretation of the Bouguer and residual gravity
anomalies. The results obtained gave us information about the basement depth and the thickness of sediment infill
of the basin. Observing the residual values of gravity anomaly field we found a large negative anomaly (-30 mGal)
under the Chad basin connected to the presence of low-density sediments. Furthermore, there are several positive
anomalies around the edges of the basin [3] and a pattern of linear negative anomalies outside of it. Both types
of trends are linked to the presence of rifts and extensional structures. Using the inversion modelling, we could
observe a deepening variation of the depth of the basement moving from the southern part (2-3 km) to the northern
(4-6 km) one of the Chad Lake. The deepening of the basement is connected to the Termit rift basin and the values
are consistent with previous seismic surveys [2]. The depth of the basement under the city of Bol is between 3
and 4 km, but unfortunately, there are no other geological/geophysical constraints to confirm these values. For
the drilling purpose, since in the inversion we used a minimum value of the density contrast (200 kg/m3) among
the range defined (200-400 kg/m3), it is possible to assume that the maximum expected depth of the basement
is about 4 km. We suggest an integrative geophysical survey, such as a seismic reflection campaign to get more
detailed information about the structure of the basement (faults, highs and lows) as well as on the variability of its
depth and the thickness of the sediment cover
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