136 research outputs found
Collapse and Bose-Einstein condensation in a trapped Bose-gas with negative scattering length
We find that the key features of the evolution and collapse of a trapped Bose
condensate with negative scattering length are predetermined by the particle
flux from the above-condensate cloud to the condensate and by 3-body
recombination of Bose-condensed atoms. The collapse, starting once the number
of Bose-condensed atoms reaches the critical value, ceases and turns to
expansion when the density of the collapsing cloud becomes so high that the
recombination losses dominate over attractive interparticle interaction. As a
result, we obtain a sequence of collapses, each of them followed by dynamic
oscillations of the condensate. In every collapse the 3-body recombination
burns only a part of the condensate, and the number of Bose-condensed atoms
always remains finite. However, it can comparatively slowly decrease after the
collapse, due to the transfer of the condensate particles to the
above-condensate cloud in the course of damping of the condensate oscillations.Comment: 11 pages, 3 figure
Three-body recombination of ultra-cold atoms to a weakly bound level
We discuss three-body recombination of ultra-cold atoms to a weakly bound
level. In this case, characterized by large and positive scattering length
for pair interaction, we find a repulsive effective potential for three-body
collisions, which strongly reduces the recombination probability and makes
simple Jastrow-like approaches absolutely inadequate. In the zero temperature
limit we obtain a universal relation, independent of the detailed shape of the
interaction potential, for the (event) rate constant of three-body
recombination: , where is the atom mass.Comment: 10 pages, 3 Postscript figure
Antiproton-Hydrogen annihilation at sub-kelvin temperatures
The main properties of the interaction of ultra low-energy antiprotons ( a.u.) with atomic hydrogen are established. They include the
elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The
inverse Auger process () is taken into account in the
framework of an unitary coupled-channels model. The annihilation cross-section
is found to be several times smaller than the predictions made by the black
sphere absorption models. A family of nearthreshold metastable
states is predicited. The dependence of Protonium formation probability on the
position of such nearthreshold S-matrix singularities is analysed. An
estimation for the annihilation cross section is obtained.Comment: latex.tar.gz file, 22 pages, 9 figure
Evolution and global collapse of trapped Bose condensates under variations of the scattering length
We develop the idea of selectively manipulating the condensate in a trapped
Bose-condensed gas, without perturbing the thermal cloud. The idea is based on
the possibility to modify the mean field interaction between atoms (scattering
length) by nearly resonant incident light or by spatially uniform change of the
trapping magnetic field. For the gas in the Thomas-Fermi regime we find
analytical scaling solutions for the condensate wavefunction evolving under
arbitrary variations of the scattering length . The change of from
positive to negative induces a global collapse of the condensate, and the final
stages of the collapse will be governed by intrinsic decay processes.Comment: 4 pages, LaTeX, other comments are at
http://WWW.amolf.nl/departments/quantumgassen/TITLE.HTM
On the stability of standing matter waves in a trap
We discuss excited Bose-condensed states and find the criterion of dynamical
stability of a kink-wise state, i.e., a standing matter wave with one nodal
plane perpendicular to the axis of a cylindrical trap. The dynamical stability
requires a strong radial confinement corresponding to the radial frequency
larger than the mean-field interparticle interaction. We address the question
of thermodynamic instability related to the presence of excitations with
negative energy.Comment: 4 pages, 3 figure
Bose-Einstein condensation in trapped dipolar gases
We discuss Bose-Einstein condensation in a trapped gas of bosonic particles
interacting dominantly via dipole-dipole forces. We find that in this case the
mean-field interparticle interaction and, hence, the stability diagram are
governed by the trapping geometry. Possible physical realisations include
ultracold heteronuclear molecules, or atoms with laser induced electric dipole
moments.Comment: 4 pages, 4 figure
Collapse dynamics of trapped Bose-Einstein condensates
We analyze the implosion and subsequent explosion of a trapped condensate
after the scattering length is switched to a negative value. Our results
compare very well qualitatively and fairly well quantitatively with the results
of recent experiments at JILA.Comment: 4 pages, 3 figure
Influence of nearly resonant light on the scattering length in low-temperature atomic gases
We develop the idea of manipulating the scattering length in
low-temperature atomic gases by using nearly resonant light. As found, if the
incident light is close to resonance with one of the bound levels of
electronically excited molecule, then virtual radiative transitions of a pair
of interacting atoms to this level can significantly change the value and even
reverse the sign of . The decay of the gas due to photon recoil, resulting
from the scattering of light by single atoms, and due to photoassociation can
be minimized by selecting the frequency detuning and the Rabi frequency. Our
calculations show the feasibility of optical manipulations of trapped Bose
condensates through a light-induced change in the mean field interaction
between atoms, which is illustrated for Li.Comment: 12 pages, 1 Postscript figur
- …