25,415 research outputs found
Characteristics of optical multi-peak solitons induced by higher-order effects in an erbium-doped fiber system
We study multi-peak solitons \textit{on a plane-wave background} in an
erbium-doped fiber system with some higher-order effects, which is governed by
a coupled Hirota and Maxwel-Bloch (H-MB) model. The important characteristics
of multi-peak solitons induced by the higher-order effects, such as the
velocity changes, localization or periodicity attenuation, and state
transitions, are revealed in detail. In particular, our results demonstrate
explicitly that a multi-peak soliton can be converted to an anti-dark soliton
when the periodicity vanishes; on the other hand, a multi-peak soliton is
transformed to a periodic wave when the localization vanishes. Numerical
simulations are performed to confirm the propagation stability of multi-peak
solitons riding on a plane-wave background. Finally, we compare and discuss the
similarity and difference of multi-peak solitons in special degenerate cases of
the H-MB system with general existence conditions.Comment: 7 pages, 4 figure
Stationary states and quantum quench dynamics of Bose-Einstein condensates in a double-well potential
We consider the properties of stationary states and the dynamics of
Bose-Einstein condensates (BECs) in a double-well (DW) potential with pair
tunneling by using a full quantum-mechanical treatment. Furthermore, we study
the quantum quench dynamics of the DW system subjected to a sudden change of
the Peierls phase. It is shown that strong pair tunneling evidently influences
the energy spectrum structure of the stationary states. For relatively weak
repulsive interatomic interactions, the dynamics of the DW system with a
maximal initial population difference evolves from Josephson oscillations to
quantum self-trapping as one increases the pair tunneling strength, while for
large repulsion the strong pair tunneling inhibits the quantum self-trapping.
In the case of attractive interatomic interactions, strong pair tunneling tends
to destroy the Josephson oscillations and quantum self-trapping, and the system
eventually enters a symmetric regime of zero population difference. Finally,
the effect of the Peierls phase on the quantum quench dynamics of the system is
analyzed and discussed. These new features are remarkably different from the
usual dynamical behaviors of a BEC in a DW potential.Comment: 9 pages,7 figures,accepted for publication in Journal of Physics
Parametric cooling of a degenerate Fermi gas in an optical trap
We demonstrate a novel technique for cooling a degenerate Fermi gas in a
crossed-beam optical dipole trap, where high-energy atoms can be selectively
removed from the trap by modulating the stiffness of the trapping potential
with anharmonic trapping frequencies. We measure the dependence of the cooling
effect on the frequency and amplitude of the parametric modulations. It is
found that the large anharmonicity along the axial trapping potential allows to
generate a degenerate Fermi gas with anisotropic energy distribution, in which
the cloud energy in the axial direction can be reduced to the ground state
value
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