935 research outputs found
Self-trapping of Bose-Einstein condensates in optical lattices
The self-trapping phenomenon of Bose-Einstein condensates (BECs) in optical
lattices is studied extensively by numerically solving the Gross-Pitaevskii
equation. Our numerical results not only reproduce the phenomenon that was
observed in a recent experiment [Anker {\it et al.}, Phys. Rev. Lett. {\bf 94}
(2005)020403], but also find that the self-trapping breaks down at long
evolution times, that is, the self-trapping in optical lattices is only
temporary. The analysis of our numerical results shows that the self-trapping
in optical lattices is related to the self-trapping of BECs in a double-well
potential. A possible mechanism of the formation of steep edges in the wave
packet evolution is explored in terms of the dynamics of relative phases
between neighboring wells.Comment: 8 pages, 15 figure
Pulse-duration dependence of high-order harmonic generation with coherent superposition state
We make a systematic study of high-order harmonic generation (HHG) in a
He-like model ion when the initial states are prepared as a coherent
superposition of the ground state and an excited state. It is found that,
according to the degree of the ionization of the excited state, the laser
intensity can be divided into three regimes in which HHG spectra exhibit
different characteristics. The pulse-duration dependence of the HHG spectra in
these regimes is studied. We also demonstrate evident advantages of using
coherent superposition state to obtain high conversion efficiency. The
conversion efficiency can be increased further if ultrashort laser pulses are
employed
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