1,570 research outputs found
Splitting times of doubly quantized vortices in dilute Bose-Einstein condensates
Recently, the splitting of a topologically created doubly quantized vortex
into two singly quantized vortices was experimentally investigated in dilute
atomic cigar-shaped Bose-Einstein condensates [Y. Shin et al., Phys. Rev. Lett.
93, 160406 (2004)]. In particular, the dependency of the splitting time on the
peak particle density was studied. We present results of theoretical
simulations which closely mimic the experimental set-up. Contrary to previous
theoretical studies, claiming that thermal excitations are the essential
mechanism in initiating the splitting, we show that the combination of
gravitational sag and time dependency of the trapping potential alone suffices
to split the doubly quantized vortex in time scales which are in good agreement
with the experiments. We also study the dynamics of the resulting singly
quantized vortices which typically intertwine--especially, a peculiar vortex
chain structure appears for certain parameter values.Comment: 5 pages, 5 figure
Universal vortex formation in rotating traps with bosons and fermions
When a system consisting of many interacting particles is set rotating, it
may form vortices. This is familiar to us from every-day life: you can observe
vortices while stirring your coffee or watching a hurricane. In the world of
quantum mechanics, famous examples of vortices are superconducting films and
rotating bosonic He or fermionic He liquids. Vortices are also observed
in rotating Bose-Einstein condensates in atomic traps and are predicted to
exist for paired fermionic atoms. Here we show that the rotation of trapped
particles with a repulsive interaction leads to a similar vortex formation,
regardless of whether the particles are bosons or (unpaired) fermions. The
exact, quantum mechanical many-particle wave function provides evidence that in
fact, the mechanism of this vortex formation is the same for boson and fermion
systems.Comment: 4 pages, 4 figure
Quantum theory of a vortex line in an optical lattice
We investigate the quantum theory of a vortex line in a stack of
weakly-coupled two-dimensional Bose-Einstein condensates, that is created by a
one-dimensional optical lattice. We derive the dispersion relation of the
Kelvin modes of the vortex line and also study the coupling between the Kelvin
modes and the quadrupole modes. We solve the coupled dynamics of the vortex
line and the quadrupole modes, both classically as well as quantum
mechanically. The quantum mechanical solution reveals the possibility of
generating nonequilibrium squeezed vortex states by strongly driving the
quadrupole modes.Comment: Minor changes in response to a referee repor
Fifty-fold improvement in the number of quantum degenerate fermionic atoms
We have produced a quantum degenerate Li-6 Fermi gas with up to 7 x 10^7
atoms, an improvement by a factor of fifty over all previous experiments with
degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic
Na-23 in the F=2, upper hyperfine ground state. We have also achieved
Bose-Einstein condensation of F=2 sodium atoms by direct evaporation
The Experimental Observation of a Superfluid Gyroscope in a dilute Bose Condensed Gas
We have observed a superfluid gyroscope effect in a dilute gas Bose-Einstein
condensate. A condensate with a vortex possesses a single quantum of angular
momentum and this causes the plane of oscillation of the scissors mode to
precess around the vortex line. We have measured the precession rate of the
scissors oscillation. From this we deduced the angular momentum associated with
the vortex line and found a value close to per particle, as predicted
for a superfluid.Comment: 4 pages 5 fig
Extinction efficiencies of coated absorbing aerosols measured by cavity ring down aerosol spectrometry
International audienceIn this study, we measure the extinction efficiency at 532 nm of absorbing aerosol particles coated with a non-absorbing solid and liquid organic shell with coating thickness varying between 5 and 100 nm using cavity ring down aerosol spectrometry. For this purpose, we use nigrosin, an organic black dye, as a model absorbing core and two non-absorbing organic substances as shells, glutaric acid (GA) and Di-Ethyl-Hexyl-Sebacate (DEHS). The measured behavior of the coated particles is consistent with Mie calculations of core-shell particles. Errors between measured and calculated values for nigrosin coated with GA and DEHS are between 0.5% and 10.5% and between 0.5% and 9%, respectively. However, it is evident that the calculations are in better agreement with the measured results for thinner coatings. Possible reasons for these discrepancies are discussed
Vortex nucleation in Bose-Einstein condensates in an oblate, purely magnetic potential
We have investigated the formation of vortices by rotating the purely
magnetic potential confining a Bose-Einstein condensate. We modified the bias
field of an axially symmetric TOP trap to create an elliptical potential that
rotates in the radial plane. This enabled us to study the conditions for vortex
nucleation over a wide range of eccentricities and rotation rates.Comment: 4 pages 4 figure
Creation of solitons and vortices by Bragg reflection of Bose-Einstein condensates in an optical lattice
We study the dynamics of Bose-Einstein condensates in an optical lattice and
harmonic trap. The condensates are set in motion by displacing the trap and
initially follow simple semiclassical paths, shaped by the lowest energy band.
Above a critical displacement, the condensate undergoes Bragg reflection. For
high atom densities, the first Bragg reflection generates a train of solitons
and vortices, which destabilize the condensate and trigger explosive expansion.
At lower densities, soliton and vortex formation requires multiple Bragg
reflections, and damps the center-of-mass motion.Comment: 5 pages including 5 figures (for higher resolution figures please
email the authors
Characteristics and oil sorption effectiveness of kapok fiber, sugarcane bagasse and rice husks: Oil removal suitability matrix
The characteristics and water/oil sorption effectiveness of kapok fiber, sugarcane bagasse and rice husks have been compared. The three biomass types are subjected to field-emission scanning electron microscopy-energy dispersive x-ray spectroscopy while the surface tension analyses for liquid-air and oil-water systems have also been conducted. Both kapok fiber and sugarcane bagasse exhibit excellent oil sorption capabilities for diesel, crude, new engine and used engine oils since all their oil sorption capacities exceed 10 g/g. Synthetic sorbent exhibits oil sorption capacities comparable to sugarcane bagasse while rice husks exhibit the lowest oil sorption capacities among all the sorbents. Kapok fiber shows overwhelmingly high oil-to-water sorption (O/W) ratios ranging from 19.35 to 201.53 while sugarcane bagasse, rice husks and synthetic sorbent have significantly lower O/W ratios (0.76 to 2.69). This suggests that kapok fiber is a highly-effectual oil sorbent even in well-mixed oil-water media. An oil sorbent suitability matrix has been proposed to aid relevant stakeholders for evaluation of customized oil removal usage of the natural sorbents
Dynamical Instability of a Doubly Quantized Vortex in a Bose-Einstein condensate
Doubly quantized vortices were topologically imprinted in Na
condensates, and their time evolution was observed using a tomographic imaging
technique. The decay into two singly quantized vortices was characterized and
attributed to dynamical instability. The time scale of the splitting process
was found to be longer at higher atom density.Comment: 5 pages, 4 figure
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