373 research outputs found
Quadrupole Oscillation of a Single-Vortex Condensate: Evidence for Kelvin Modes
We study the two transverse quadrupole modes of a cigar-shaped Bose-Einstein
condensate with a single centered vortex. We show that the counter-rotating
mode is more strongly damped than in the absence of a vortex, whereas the
co-rotating mode is not affected appreciably by the vortex. We interpret this
result as a decay of the counter-rotating quadrupole mode into two excitations
of the vortex line, the so-called Kelvin modes. This is supported by direct
observation of the wiggling vortex line.Comment: 4 pages, 3 figure
Precision Mass Measurements of 129-131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process
Masses adjacent to the classical waiting-point nuclide 130Cd have been
measured by using the Penning- trap spectrometer ISOLTRAP at ISOLDE/CERN. We
find a significant deviation of over 400 keV from earlier values evaluated by
using nuclear beta-decay data. The new measurements show the reduction of the N
= 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated
with the ejected wind from type-II supernovae as well as from compact object
binary mergers is studied, by using state-of-the-art hydrodynamic simulations.
We find a consistent and direct impact of the newly measured masses on the
calculated abundances in the A = 128 - 132 region and a reduction of the
uncertainties from the precision mass input data
Probing the N = 32 shell closure below the magic proton number Z = 20: Mass measurements of the exotic isotopes 52,53K
The recently confirmed neutron-shell closure at N = 32 has been investigated
for the first time below the magic proton number Z = 20 with mass measurements
of the exotic isotopes 52,53K, the latter being the shortest-lived nuclide
investigated at the online mass spectrometer ISOLTRAP. The resulting
two-neutron separation energies reveal a 3 MeV shell gap at N = 32, slightly
lower than for 52Ca, highlighting the doubly-magic nature of this nuclide.
Skyrme-Hartree-Fock-Boguliubov and ab initio Gorkov-Green function calculations
are challenged by the new measurements but reproduce qualitatively the observed
shell effect.Comment: 5 pages, 5 figure
In-situ velocity imaging of ultracold atoms using slow--light
The optical response of a moving medium suitably driven into a slow-light
propagation regime strongly depends on its velocity. This effect can be used to
devise a novel scheme for imaging ultraslow velocity fields. The scheme turns
out to be particularly amenable to study in-situ the dynamics of collective and
topological excitations of a trapped Bose-Einstein condensate. We illustrate
the advantages of using slow-light imaging specifically for sloshing
oscillations and bent vortices in a stirred condensate
Critical rotation of a harmonically trapped Bose gas
We study experimentally and theoretically a cold trapped Bose gas under
critical rotation, i.e. with a rotation frequency close to the frequency of the
radial confinement. We identify two regimes: the regime of explosion where the
cloud expands to infinity in one direction, and the regime where the condensate
spirals out of the trap as a rigid body. The former is realized for a dilute
cloud, and the latter for a Bose-Einstein condensate with the interparticle
interaction exceeding a critical value. This constitutes a novel system in
which repulsive interactions help in maintaining particles together.Comment: 4 pages, 4 figures, submitted to PR
An Optical Lattice Clock with Spin-polarized 87Sr Atoms
We present a new evaluation of an 87Sr optical lattice clock using spin
polarized atoms. The frequency of the 1S0-3P0 clock transition is found to be
429 228 004 229 873.6 Hz with a fractional accuracy of 2.6 10^{-15}, a value
that is comparable to the frequency difference between the various primary
standards throughout the world. This measurement is in excellent agreement with
a previous one of similar accuracy
Surface modes of ultracold atomic clouds with very large number of vortices
We study the surface modes of some of the vortex liquids recently found by
means of exact diagonalizations in systems of rapidly rotating bosons. In
contrast to the surface modes of Bose condensates, we find that the surface
waves have a frequency linear in the excitation angular momentum, . Furthermore, in analogy with the edge waves of electronic quantum Hall
states, these excitations are {\it chiral}, that is, they can be excited only
for values of that increase the total angular momentum of the vortex
liquid. However, differently from the quantum Hall phenomena for electrons, we
also find other excitations that are approximately degenerate in the laboratory
frame with the surface modes, and which decrease the total angular momentum by
quanta. The surface modes of the Laughlin, as well as other scalar and
vector boson states are analyzed, and their {\it observable} properties
characterized. We argue that measurement of the response of a vortex liquid to
a weak time-dependent potential that imparts angular momentum to the system
should provide valuable information to characterize the vortex liquid. In
particular, the intensity of the signal of the surface waves in the dynamic
structure factor has been studied and found to depend on the type of vortex
liquid. We point out that the existence of surface modes has observable
consequences on the density profile of the Laughlin state. These features are
due to the strongly correlated behavior of atoms in the vortex liquids. We
point out that these correlations should be responsible for a remarkable
stability of some vortex liquids with respect to three-body losses.Comment: 28 pages + 6 EPS figures. Final version as accepted for publication
in Phys. Rev.
High-precision mass measurements in the rare-earth region to investigate the proton-neutron interaction
The transverse breathing mode of an elongated Bose-Einstein condensate
We study experimentally the transverse monopole mode of an elongated rubidium
condensate. Due to the scaling invariance of the non-linear Schr\"odinger
(Gross-Pitaevski) equation, the oscillation is monochromatic and sinusoidal at
short times, even under strong excitation. For ultra-low temperatures, the
quality factor can exceed 2000, where and
are the mode angular frequency and damping rate. This value is much
larger than any previously reported for other eigenmodes of a condensate. We
also present the temperature variation of and .Comment: 4 pages, 4 figures, submitted to PR
Split-merge cycle, fragmented collapse, and vortex disintegration in rotating Bose-Einstein condensates with attractive interactions
The dynamical instabilities and ensuing dynamics of singly- and
doubly-quantized vortex states of Bose-Einstein condensates with attractive
interactions are investigated using full 3D numerical simulations of the
Gross-Pitaevskii equation. With increasing the strength of attractive
interactions, a series of dynamical instabilities such as quadrupole, dipole,
octupole, and monopole instabilities emerge. The most prominent instability
depends on the strength of interactions, the geometry of the trapping
potential, and deviations from the axisymmetry due to external perturbations.
Singly-quantized vortices split into two clusters and subsequently undergo
split-merge cycles in a pancake-shaped trap, whereas the split fragments
immediately collapse in a spherical trap. Doubly-quantized vortices are always
unstable to disintegration of the vortex core. If we suddenly change the
strength of interaction to within a certain range, the vortex splits into three
clusters, and one of the clusters collapses after a few split-merge cycles. The
vortex split can be observed using a current experimental setup of the MIT
group.Comment: 11 pages, 10 figure
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