Density oscillations in trapped dipolar condensates

We investigated the ground state wave function and free expansion of a trapped dipolar condensate. We find that dipolar interaction may induce both biconcave and dumbbell density profiles in, respectively, the pancake- and cigar-shaped traps. On the parameter plane of the interaction strengths, the density oscillation occurs only when the interaction parameters fall into certain isolated areas. The relation between the positions of these areas and the trap geometry is explored. By studying the free expansion of the condensate with density oscillation, we show that the density oscillation is detectable from the time-of-flight image.Comment: 7 pages, 9 figure

Coherent population trapping and dynamical instability in the nonlinearly coupled atom-molecule system

We study the possibility of creating a coherent population trapping (CPT) state, involving free atomic and ground molecular condensates, during the process of associating atomic condensate into molecular condensate. We generalize the Bogoliubov approach to this multi-component system and study the collective excitations of the CPT state in the homogeneous limit. We develop a set of analytical criteria based on the relationship among collisions involving atoms and ground molecules, which are found to strongly affect the stability properties of the CPT state, and use it to find the stability diagram and to systematically classify various instabilities in the long-wavelength limit.Comment: 11 pages, 8 figure

Creating stable molecular condensate using a generalized Raman adiabatic passage scheme

We study the Feshbach resonance assisted stimulated adiabatic passage of an effective coupling field for creating stable molecules from atomic Bose condensate. By exploring the properties of the coherent population trapping state, we show that, contrary to the previous belief, mean-field shifts need not to limit the conversion efficiency as long as one chooses an adiabatic passage route that compensates the collision mean-field phase shifts and avoids the dynamical unstable regime.Comment: 4+\epsilon pages, 3 figure

Properties of a coupled two species atom-heteronuclear molecule condensate

We study the coherent association of a two-species atomic condensate into a condensate of heteronuclear diatomic molecules, using both a semiclassical treatment and a quantum mechanical approach. The differences and connections between the two approaches are examined. We show that, in this coupled nonlinear atom-molecule system, the population difference between the two atomic species plays a significant role in the ground-state stability properties as well as in coherent population oscillation dynamics.Comment: 7 pages, 4 figure

Fermionic R-operator approach for the small-polaron model with open boundary condition

Exact integrability and algebraic Bethe ansatz of the small-polaron model with the open boundary condition are discussed in the framework of the quantum inverse scattering method (QISM). We employ a new approach where the fermionic R-operator which consists of fermion operators is a key object. It satisfies the Yang-Baxter equation and the reflection equation with its corresponding K-operator. Two kinds of 'super-transposition' for the fermion operators are defined and the dual reflection equation is obtained. These equations prove the integrability and the Bethe ansatz equation which agrees with the one obtained from the graded Yang-Baxter equation and the graded reflection equations.Comment: 10 page

Measurement back-action on the quantum spin-mixing dynamics of a spin-1 Bose-Einstein condensate

We consider a small F=1 spinor condensate inside an optical cavity driven by an optical probe field, and subject the output of the probe to a homodyne detection, with the goal of investigating the effect of measurement back-action on the spin dynamics of the condensate. Using the stochastic master equation approach, we show that the effect of back-action is sensitive to not only the measurement strength but also the quantum fluctuation of the spinor condensate. The same method is also used to estimate the atom numbers below which the effect of back-action becomes so prominent that extracting spin dynamics from this cavity-based detection scheme is no longer practical

Does stability of relativistic dissipative fluid dynamics imply causality?

We investigate the causality and stability of relativistic dissipative fluid dynamics in the absence of conserved charges. We perform a linear stability analysis in the rest frame of the fluid and find that the equations of relativistic dissipative fluid dynamics are always stable. We then perform a linear stability analysis in a Lorentz-boosted frame. Provided that the ratio of the relaxation time for the shear stress tensor, $\tau_\pi$, to the sound attenuation length, $\Gamma_s = 4\eta/3(\varepsilon+P)$, fulfills a certain asymptotic causality condition, the equations of motion give rise to stable solutions. Although the group velocity associated with perturbations may exceed the velocity of light in a certain finite range of wavenumbers, we demonstrate that this does not violate causality, as long as the asymptotic causality condition is fulfilled. Finally, we compute the characteristic velocities and show that they remain below the velocity of light if the ratio $\tau_\pi/\Gamma_s$ fulfills the asymptotic causality condition.Comment: 30 pages, 10 figures

Three-Gorges Dam Fine Sediment Pollutant Transport: Turbulence SPH Model Simulation of Multi-Fluid Flows

YesThe Three Gorges Dam (TGD) constructed at the Yangtze River, China represents a revolutionary project to battle against the mage-scale flooding problems while improving the local economy at the same time. However, the large-scale fine-size sediment and pollutant material transport caused by the TGD operation are found to be inevitable and long-lasting. In this paper, a multi-fluid Incompressible Smoothed Particle Hydrodynamics (ISPH) model is used to simulate the multi-fluid flows similar to the fine sediment materials transport (in muddy flows) and water flow mixing process. The SPH method is a mesh-free particle modeling approach that can treat the free surfaces and multi-interfaces in a straightforward manner. The proposed model is based on the universal multi-fluid flow equations and a unified pressure equation is used to account for the interaction arising from the different fluid components. A Sub-Particle-Scale (SPS) turbulence model is included to address the turbulence effect generated during the flow process. The proposed model is used to investigate two cases of multi-fluid flows generated from the polluted flow intrusions into another fluid. The computations are found in good agreement with the practical situations. Sensitivity studies have also been carried out to evaluate the particle spatial resolution and turbulence modeling on the flow simulations. The proposed ISPH model could provide a promising tool to study the practical multi-fluid flows in the TGD operation environment.The Major State Basic Research Development Program (973 program) of China (No. 2013CB036402) and the National Natural Science Foundation of China (No. 51479087)