4,017 research outputs found
Josephson Oscillation and Transition to Self-Trapping for Bose-Einstein-Condensates in a Triple-Well Trap
We investigate the tunnelling dynamics of Bose-Einstein-Condensates(BECs) in
a symmetric as well as in a tilted triple-well trap within the framework of
mean-field treatment. The eigenenergies as the functions of the zero-point
energy difference between the tilted wells show a striking entangled star
structure when the atomic interaction is large. We then achieve insight into
the oscillation solutions around the corresponding eigenstates and observe
several new types of Josephson oscillations. With increasing the atomic
interaction, the Josephson-type oscillation is blocked and the self-trapping
solution emerges. The condensates are self-trapped either in one well or in two
wells but no scaling-law is observed near transition points. In particular, we
find that the transition from the Josephson-type oscillation to the
self-trapping is accompanied with some irregular regime where tunnelling
dynamics is dominated by chaos. The above analysis is facilitated with the help
of the Poicar\'{e} section method that visualizes the motions of BECs in a
reduced phase plane.Comment: 10 pages, 11 figure
Periodic Modulation Effect on Self-Trapping of Two weakly coupled Bose-Einstein Condensates
With phase space analysis approach, we investigate thoroughly the
self-trapping phenomenon for two weakly coupled Bose-Einstein condensates (BEC)
in a symmetric double-well potential. We identify two kinds of self-trapping by
their different relative phase behavior. With applying a periodic modulation on
the energy bias of the system we find the occurrence of the self-trapping can
be controlled, saying, the transition parameters can be adjusted effectively by
the periodic modulation. Analytic expressions for the dependence of the
transition parameters on the modulation parameters are derived for high and low
frequency modulations. For an intermediate frequency modulation, we find the
resonance between the periodic modulation and nonlinear Rabi oscillation
dramatically affects the tunnelling dynamics and demonstrate many novel
phenomena. Finally, we study the effects of many-body quantum fluctuation on
self-trapping and discuss the possible experimental realization of the model.Comment: 7 pages, 11 figure
Many-Body Effects on Nonadiabatic Feshbach Conversion in Bosonic Systems
We investigate the dynamics of converting cold bosonic atoms to molecules
when an external magnetic field is swept across a Feshbach resonance. Our
analysis relies on a zero temperature quantum microscopic model that accounts
for many-body effects, triggering the association process. We show that the
picture of two-body molecular production depicted by Landau-Zener model is
significantly altered due to many-body effects. In nonadiabatic regime, we
derive an analytic expression for molecular conversion efficiency that explains
the discrepancy between the prediction of Landau-Zener formula and experimental
data[Hodby et al., Phys. Rev. Lett. {\bf 94}, 120402 (2005)]. Our theory is
further extended to the formation of heteronuclear diatomic molecules and gives
some interesting predictions.Comment: 7pages 5figure
Rosen-Zener interferometry with Ultracold Atoms
We propose a time-domain "interferometer" based on ultracold Bose atoms
loaded on a double well potential. By the adiabatic Rosen-Zener process, the
barrier between two wells is ramped down slowly, held for a while, then ramped
back. Starting with a coherent state of double well system, the final
occupations on one well show interesting interference fringes in the
time-domain. The fringe pattern is sensitive to the initial state, the
interatomic interaction, and the external forces such as gravity which can
change the shape of the double well. In this sense, this interferometric scheme
has the potentials for precision measurements with ultracold atoms. The
underlying mechanism is revealed and possible applications are discussed.Comment: 4 pages, 5 figure
Semi-Numerical Simulation of Reionization with Semi-Analytical Modeling of Galaxy Formation
In a semi-numerical model of reionization, the evolution of ionization
fraction is simulated approximately by the ionizing photon to baryon ratio
criterion. In this paper we incorporate a semi-analytical model of galaxy
formation based on the Millennium II N-body simulation into the semi-numerical
modeling of reionization. The semi-analytical model is used to predict the
production of ionizing photons, then we use the semi-numerical method to model
the reionization process. Such an approach allows more detailed modeling of the
reionization, and also connects observations of galaxies at low and high
redshifts to the reionization history. The galaxy formation model we use was
designed to match the low- observations, and it also fits the high redshift
luminosity function reasonably well, but its prediction on the star formation
falls below the observed value, and we find that it also underpredicts the
stellar ionizing photon production rate, hence the reionization can not be
completed at without taking into account some other potential
sources of ionization photons. We also considered simple modifications of the
model with more top heavy initial mass functions (IMF), with which the
reionization can occur at earlier epochs. The incorporation of the
semi-analytical model may also affect the topology of the HI regions during the
EoR, and the neutral regions produced by our simulations with the
semi-analytical model appeared less poriferous than the simple halo-based
models.Comment: 13 pages, 8 figures, RAA accepte
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