5,653 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
Mean-field model for Josephson oscillation in a Bose-Einstein condensate on an one-dimensional optical trap
Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study
the phase coherence in a repulsive Bose-Einstein condensate (BEC) trapped by a
harmonic and an one-dimensional optical lattice potential to describe the
experiment by Cataliotti {\it et al.} on atomic Josephson oscillation [Science
{\bf 293}, 843 (2001)]. The phase coherence is maintained after the BEC is set
into oscillation by a small displacement of the magnetic trap along the optical
lattice. The phase coherence in the presence of oscillating neutral current
across an array of Josephson junctions manifests in an interference pattern
formed upon free expansion of the BEC. The numerical response of the system to
a large displacement of the magnetic trap is a classical transition from a
coherent superfluid to an insulator regime and a subsequent destruction of the
interference pattern in agreement with the more recent experiment by Cataliotti
{\it et al.} [e-print cond-mat/0207139].Comment: 6 Latex pages, 6 PS and EPS figures, Accepted in European Physical
Journal
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
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
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