8,120 research outputs found
Josephson oscillation and induced collapse in an attractive Bose-Einstein condensate
Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study
the Josephson oscillation of an attractive Bose-Einstein condensate (BEC) in a
one-dimensional periodic optical-lattice potential. We find that the Josephson
frequency is virtually independent of the number of atoms in the BEC and of the
inter-atomic interaction (attractive or repulsive). We study the dependence of
Josephson frequency on the laser wave length and the strength of the
optical-lattice potential. For a fixed laser wave length (795 nm), the
Josephson frequency decreases with increasing strength as found in the
experiment of Cataliotti {\it et al.} [Science {\bf 293}, 843 (2001)]. For a
fixed strength, the Josephson frequency remains essentially unchanged for a
reasonable variation of laser wave length around 800 nm. However, for a fixed
strength, the Josephson oscillation is disrupted with the increase of laser
wave length beyond 2000 nm leading to a collapse of a sufficiently attractive
BEC. These features of Josephson oscillation can be tested experimentally with
present set ups.Comment: 7 pages, 12 ps and eps figures, Physical Review
Finite-well potential in the 3D nonlinear Schroedinger equation: Application to Bose-Einstein condensation
Using variational and numerical solutions we show that stationary
negative-energy localized (normalizable) bound states can appear in the
three-dimensional nonlinear Schr\"odinger equation with a finite square-well
potential for a range of nonlinearity parameters. Below a critical attractive
nonlinearity, the system becomes unstable and experiences collapse. Above a
limiting repulsive nonlinearity, the system becomes highly repulsive and cannot
be bound. The system also allows nonnormalizable states of infinite norm at
positive energies in the continuum. The normalizable negative-energy bound
states could be created in BECs and studied in the laboratory with present
knowhow.Comment: 8 pages, 12 figure
Stability and collapse of fermions in a binary dipolar boson-fermion 164Dy-161Dy mixture
We suggest a time-dependent mean-field hydrodynamic model for a binary
dipolar boson-fermion mixture to study the stability and collapse of fermions
in the Dy-Dy mixture. The condition of stability of the dipolar
mixture is illustrated in terms of phase diagrams. A collapse is induced in a
disk-shaped stable binary mixture by jumping the interspecies contact
interaction from repulsive to attractive by the Feshbach resonance technique.
The subsequent dynamics is studied by solving the time-dependent mean-field
model including three-body loss due to molecule formation in boson-fermion and
boson-boson channels. Collapse and fragmentation in the fermions after
subsequent explosions are illustrated. The anisotropic dipolar interaction
leads to anisotropic fermionic density distribution during collapse. The
present study is carried out in three-dimensional space using realistic values
of dipolar and contact interactions
Demixing and symmetry breaking in binary dipolar Bose-Einstein condensate solitons
We demonstrate fully demixed (separated) robust and stable bright binary
dipolar Bose-Einstein condensate soliton in a quasi-one-dimensional setting
formed due to dipolar interactions for repulsive contact interactions. For
large repulsive interspecies contact interaction the first species may
spatially separate from the second species thus forming a demixed
configuration, which can be spatially-symmetric or symmetry-broken. In the
spatially-symmetric case, one of the the species occupies the central region,
whereas the other species separates into two equal parts and stay predominantly
out of this central region. In the symmetry-broken case, the two species stay
side by side. Stability phase diagrams for the binary solitons are obtained.
The results are illustrated with realistic values of parameters in the binary
164Dy-168Er and 164Dy-162Dy mixtures. The demixed solitons are really soliton
molecules formed of two types of atoms. A proposal for creating dipolar
solitons in experiments is also presented
Self trapping of a dipolar Bose-Einstein condensate in a double well
We study the Josephson oscillation and self trapping dynamics of a
cigar-shaped dipolar Bose-Einstein condensate of Cr atoms polarized
along the symmetry axis of an axially-symmetric double-well potential using the
numerical solution of a mean-field model, for dominating repulsive contact
interaction (large positive scattering length a) over an anisotropic dipolar
interaction. Josephson-type oscillation emerges for small and very large number
of atoms, whereas self trapping is noted for an intermediate number of atoms.
The dipolar interaction pushes the system away from self trapping towards
Josephson oscillation. We consider a simple two-mode description for a
qualitative understanding of the dynamics
Dipolar Bose-Einstein condensate in a ring or in a shell
We study properties of a trapped dipolar Bose-Einstein condensate (BEC) in a
circular ring or a spherical shell using the mean-field Gross-Pitaevskii
equation. In the case of the ring-shaped trap we consider different
orientations of the ring with respect to the polarization direction of the
dipoles. In the presence of long-range anisotropic dipolar and short-range
contact interactions, the anisotropic density distribution of the dipolar BEC
in both traps is discussed in detail. The stability condition of the dipolar
BEC in both traps is illustrated in phase plot of dipolar and contact
interactions. We also study and discuss the properties of a vortex dipolar BEC
in these traps
Stable, mobile, dark-in-bright, dipolar Bose-Einstein condensate soliton
We demonstrate robust, stable, mobile, quasi-one-dimensional, dark-in-bright
dipolar Bose-Einstein condensate (BEC) soliton with a notch in the central
plane formed due to dipolar interaction for repulsive contact interaction. At
medium velocity the head on collision of two such solitons is found to be quasi
elastic with practically no deformation. A proposal for creating dipolar
dark-in-bright solitons in laboratories by phase imprinting is also discussed.
A rich variety of such solitons can be formed in dipolar binary BEC, where one
can have a dark-in-bright soliton coupled to a bright soliton or two coupled
dark-in-bright solitons. The findings are illustrated using numerical
simulation in three spatial dimensions employing realistic interaction
parameters for a dipolar 164Dy BEC and a binary 164Dy-162Dy BEC.Comment: arXiv admin note: text overlap with arXiv:1401.318
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