8,522 research outputs found
All-optical production of 7Li Bose-Einstein condensation using Feshbach resonances
We show an all-optical method of making 7Li condensate using tunability of
the scattering length in the proximity of a Feshbach resonance. We report the
observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow
(broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G).
Position of the scattering length zero crossing between the resonances is found
at 836 +- 4 G. The broad resonance is shown to be favorable for run away
evaporation which we perform in a crossed-beam optical dipole trap. Starting
directly form the phase space density of a magneto-optical trap we observe a
Bose-Einstein condensation threshold in less than 3 s of forced evaporation.Comment: 5 pages, 5 figure
Theory of elastic interaction between colloidal particles in the nematic cell in the presence of the external electric or magnetic field
The Green function method developed in Ref.[S. B. Chernyshuk and B. I. Lev,
Phys. Rev. E \textbf{81}, 041707 (2010)] is used to describe elastic
interactions between axially symmetric colloidal particles in the nematic cell
in the presence of the external electric or magnetic field. General formulas
for dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions in
the homeotropic and planar nematic cells with parallel and perpendicular field
orientations are obtained. A set of new results has been predicted: 1)
\textit{Deconfinement effect} for dipole particles in the homeotropic nematic
cell with negative dielectric anisotropy and perpendicular
to the cell electric field, when electric field is approaching it's Frederiks
threshold value . This means cancellation of the
confinement effect found in Ref. [M.Vilfan et al. Phys.Rev.Lett. {\bf 101},
237801, (2008)] for dipole particles near the Frederiks transition while it
remains for quadrupole particles. 2) New effect of \textit{attraction and
stabilization} of the particles along the electric field parallel to the cell
planes in the homeotropic nematic cell with . The minimun
distance between two particles depends on the strength of the field and can be
ordinary for . 3) Attraction and repulsion zones for all elastic interactions
are changed dramatically under the action of the external field.Comment: 15 pages, 17 figure
Absence of dynamical localization in interacting driven systems
Using a numerically exact method we study the stability of dynamical
localization to the addition of interactions in a periodically driven isolated
quantum system which conserves only the total number of particles. We find that
while even infinitesimally small interactions destroy dynamical localization,
for weak interactions density transport is significantly suppressed and is
asymptotically diffusive, with a diffusion coefficient proportional to the
interaction strength. For systems tuned away from the dynamical localization
point, even slightly, transport is dramatically enhanced and within the largest
accessible systems sizes a diffusive regime is only pronounced for sufficiently
small detunings.Comment: Scipost resubmission. 14 pages, 4 figures. Changes to the figures.
Corrects a few typo
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