The quantum tunneling between two-component Bose-Einstein condensates in a double-well configuration

In terms of exact solution of the time-dependent Schrodinger equation. we examine the quantum tunneling process in Bose condensates of two interacting species trapped in a double well configuration. We use the two series of time-dependent SU(2) gauge transformation to diagonalize the Hamilton operator obtain analytic time-evolution formulas of the population imbalance and the berry phase. The particle population imbalance (a(L)(+)a(L) - a(R)(+)a(R)) of species A between the two wells is studied analytically.

Quantum transport from the perspective of quantum open systems

By viewing the non-equilibrium transport setup as a quantum open system, we propose a reduced-density-matrix based quantum transport formalism. At the level of self-consistent Born approximation, it can precisely account for the correlation between tunneling and the system internal many-body interaction, leading to certain novel behavior such as the non-equilibrium Kondo effect. It also opens a new way to construct time-dependent density functional theory for transport through large-scale complex systems. (c) 2006 Elsevier B.V. All rights reserved.

Degenerate four-wave-mixing signals from dc- and ac-driven semiconductor superlattice

Within the one-dimensional tight-binding model;rnd chi-3 approximation, we have calculated four-wave-mixing (FWM) signals for a semiconductor superlattice in the presence of both static and high-frequency electric fields. When the exciton effect is negligible, the time-periodic field dynamically delocalizes the otherwise localized Wannier-Stark states, and accordingly quasienergy band structures are formed, and manifest in the FWM spectra as a series of equally separated continua. The width of each continuum is proportional to the joint width of the valence and conduction minibands and is independent of the Wannier-Stark index. The realistic homogeneous broadening blurs the continua into broad peaks, whose line shapes, far from the Lorentzian, vary with the delay time in the FWM spectra. The swinging range of the peaks is just the quasienergy bandwidth. The dynamical delocalization (DDL) also induces significant FWM signals well beyond the excitation energy window. When the Coulomb interaction is taken into account, the unequal spacing between the excitonic Wannier-Stark levels weakens the DDL effect, and the FWM spectrum is transformed into groups of discrete lines. Strikingly, the groups are evenly spaced by the ac field frequency, reflecting the characteristic of the quasienergy states. The homogeneous broadening again smears out the line structures, leading to the excitonic FWM spectra quite similar to those without the exciton effect. However, all these features predicted by the dynamical theory do not appear in a recent experiment [Phys. Rev. Lett. 79, 301 (1997)], in which, by using the static approximation the observed Wannier-Stark ladder with delay-time-dependent spacing in the FWM spectra is attributed to a temporally periodic dipole field, produced by the Bloch oscillation of electrons in real space. The contradiction between the dynamical theory and the experiments is discussed. In addition, our calculation indicates that the dynamical localization coherently enhances the time-integrated FWM signals. The feasibility of using such a technique to study the dynamical localization phenomena is shown. [S0163-1829(99)10607-6].

Observation of quantum beat in Rb by parametric four-wave mixing

Two coupled parametric four-wave-mixing processed in Rb atoms are studied using perturbation theory, which reveals clear evidence of the appearance of quantum beat at 608 cm(-1), corresponding to the energy difference of the 7s - 5d states of Rb atoms, in the parametric four-wave-mixing signals. A pump-probe technique is utilized to observe the quantum beat. Time-varying characteristics of the quantum beat are investigated using time-dependent Fourier transform. The results show that the time-varying characteristics of the quantum beat potential tool for monitoring the dissociation of molecules.

Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

Thermocapillary migrations of drops and bubbles

The transport phenomenon of drops or bubbles is a very important topic in fundamental hydrodynamics research and practical applications such as material processing and the chemical engineering. In microgravity environment, if drops or bubbles stay in a continuous phase with non-uniform temperature ¯eld, they will start to move as a result of the variance of the interface tension. This kind of movement is called the Marangoni migration. This review tries to sum up the main results in this ¯eld on theoretical analysis, numerical simulations and experiments. So far the theoretical analysis is still limited to the linear or weak nonlinear steady questions, while the current numerical simulations can already obtain the time- dependent process of the bubble/drop migration when the e®ect of heat convection is small. For strong heat convection problem, or when the Marangoni number is bigger than 100, no numerical result is in consistence with those of experiments so far. Some of the lastest numerical results are shown when heat convection is strong, and the main di®erence between strong and weak heat convection is analyzed. Finally, we also discuss the main unresolved problems in this ¯eld and some possible directions in the future.

Comparison of aggregation behaviors between branched and linear block polyethers: MesoDyn simulation study

The comparison of aggregation behaviors between the branched block polyether T1107 (polyether A) and linear polyether (EO)(60)(PO)(40)(EO)(60) (polyether B) in aqueous solution are investigated by the MesoDyn simulation. Polyether A forms micelles at lower concentration and has a smaller aggregation number than B. Both the polyethers show the time-dependent micellar growth behaviors. The spherical micelles appear and then change to rod-like micelles with time evolution in the 10 vol% solution of polyether A. The micellar cluster appears and changes to pseudo-spherical micelles with time evolution in the 20 vol% solution of polyether A. However, the spherical micelles appear and change to micellar cluster with time evolution in the 20 vol% polyether B solution. The shear can induce the micellar transition of both block polyethers. When the shear rate is 1x10(5) s(-1), the shear can induce the sphere-to-rod transition of both polyethers at the concentration of 10 and 20 vol%. When the shear rate is lower than 1x10(5) s(-1), the huge micelles and micellar clusters can be formed in the 10 and 20 vol% polyether A systems under the shear, while the huge micelles are formed and then disaggregated with the time evolution in the 20 vol% polyether B system.

Period-doubling bifurcations of the thermocapillary convection in a floating half zone

This study experimentally explored the fine structures of the successive period-doubling bifurcations of the time-dependent thermocapillary convection in a floating half zone of 10 cSt silicone oil with the diameter d (0)=3.00 mm and the aspect ratio A=l/d (0)=0.72 in terrestrial conditions. The onset of time-dependent thermocapillary convection predominated in this experimental configuration and its subsequent evolution were experimentally detected through the local temperature measurements. The experimental results revealed a sequence of period-doubling bifurcations of the time-dependent thermocapillary convection, similar in some way to one of the routes to chaos for buoyant natural convection. The critical frequencies and the corresponding fractal frequencies were extracted through the real-time analysis of the frequency spectra by Fast-Fourier-Transformation (FFT). The projections of the trajectory onto the reconstructed phase-space were also provided. Furthermore, the experimentally predicted Feigenbaum constants were quite close to the theoretical asymptotic value of 4.669 [Feigenbaum M J. Phys Lett A, 1979, 74: 375-378].

Dynamics of morphological changes for mitochondrial fission and fusion

Mitochondria experience continuous fusion and fission in a living cell, but their dynamics remains poorly quantified. Here a theoretical model was developed, upon a simplified population balance equation (PBE), to predict the morphological changes induced by mitochondrial fission and fusion. Assuming that both fission and fusion events are statistically independent, the survival probability of mitochondria staying in the fission or fusion state was formulated as an exponentially-decayed function with time, which depended on the time-dependent distribution of the mitochondrial volume and the fission and fusion rates. Parametric analysis was done for two typical volume distributions. One was Gamma distribution and the other was Gaussian distribution, derived from the measurements of volume distribution for individual mitochondria in a living cell and purified mitochondria in vitro. The predictions indicated that the survival probability strongly depended on morphological changes of individual mitochondria and was inversely correlated to the fission and fusion rates. This work provided a new insight into quantifying the mitochondrial dynamics via monitoring the evolution of the mitochondrial volume.

Effect of Nozzle Temperature on the Performance of a 1 kW H2-N2 Arcjet Thruster

A 1 kW-class arcjet thruster was ¯red in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 : N2 = 2.8 : 1.5 in volume at a total °ow rate of 4.3 slm was used as the propellant with an input power ¯xed at 860 W. The time-dependent thrust, nozzle temperature and inlet pressure of the propellant were measured simultaneously. Results showed that with the increase in nozzle temperature the thrust decreased and various losses increased. The physical mechanisms involved in these effects are discussed.

Isolated sub-30-as pulse generation of an He+ ion by an intense few-cycle chirped laser and its high-order harmonic pulses

We present an efficient method to generate a ultrashort attosecond (as) pulse when a model He+ ion is exposed to the combination of an intense few-cycle chirped laser pulse and its 27th harmonics. By solving the time-dependent Schroumldinger equation, we found that high-order harmonic generation (HHG) from He+ ion is enhanced by seven orders of magnitude due to the presence of the harmonic pulse. After optimizing the chirp of the fundamental pulse, we show that the cut-off energy of the generated harmonics is extended effectively to I-p+25.5U(p). As a result, an isolated 26-as pulse with a bandwidth of 170.5 eV can be obtained directly from the supercontinuum around the cut-off of HHG. To better understand the physical origin of HHG enhancement and attosecond pulse emission, we perform semiclassical simulations and analyze the time-frequency characteristics of attosecond pulse.

Topological objects in the O(3) nonlinear sigma model

We study the topological defects in the nonlinear O(3) sigma model in terms of the decomposition of U(1) gauge potential. Time-dependent baby skyrmions are discussed in the (2 + 1)-dimensional spacetime with the CP1 field. Furthermore, we show that there are three kinds of topological defects-vortex lines, point defects and knot exist in the (3 + 1)-dimensional model, and their topological charges, locations and motions are determined by the phi-mapping topological current theory.

Topological objects in two-gap superconductor

We discuss the non-Abelian topological objects, in particular the non-Abrikosov vortex and the magnetic knot made of the twisted non-Abrikosov vortex, in two-gap superconductor. We show that there are two types of non-Abrikosov vortex in Ginzburg-Landau theory of two-gap superconductor, the D-type which has no concentration of the condensate at the core and the N-type which has a non-trivial profile of the condensate at the core, under a wide class of realistic interaction potential. We prove that these non-Abrikosov vortices can have either integral or fractional magnetic flux, depending on the interaction potential. We show that they are described by the non-Abelian topology pi(2)(S-2) and pi(1)(S-1), in addition to the well-known Abelian topology pi(1)(S-1). Furthermore, we discuss the possibility to construct a stable magnetic knot in two-gap superconductor by twisting the non-Abrikosov vortex and connecting two periodic ends together, whose knot topology pi(3)(S-2) is described by the Chern-Simon index of the electromagnetic potential. We argue that similar topological objects may exist in multi-gap or multi-layer superconductors and multi-component Bose-Einstein condensates and superfluids, and discuss how these topological objects can be constructed in MgB2, Sr2RuO4, He-3, and liquid metallic hydrogen.

Optical absorption spectra of Na-5, Na-6 and Na-7 clusters: a theoretical study

In the frame of time-dependent density functional theory, the: dynamical polarizabilities of Na-5, Na-6 and Na-7 clusters are calculated using a time-dependent local density approximation. By using Fourier transformation, the optical absorption spectra of Na-5, Na-6 and Na-7 clusters are obtained from their dynamical polarizabilities. It is shown that experimentally measured optical absorption spectra of Na-5, Na-6 and Na-7 clusters are reproduced in our calculations. Furthermore, the calculations of Na-6 and Na-7 clusters are in good agreement with the results of configuration interaction method. Compared with the three-dimensional structure of Na-6, the calculated optical absorption spectra of Na-6 with the two-dimensional structure are more close to the experimental data.

High-order harmonic generation and multi-photon ionization of Na-2 in laser fields

In this paper high-order harmonic generation (HHG) spectra and the ionization probabilities of various charge states of small cluster Na-2 in the multiphoton regimes are calculated by using time-dependent local density approximation (TDLDA) for one-colour (1064 nm) and two-colour (1064 nm and 532 nm) ultrashort (25 fs) laser pulses. HHG spectra of Na2 have not the large extent of plateaus due to pronounced collective effects of electron dynamics. In addition, the two-colour laser field can result in the breaking of the symmetry and generation of the even order harmonic such as the second order harmonic. The results of ionization probabilities show that a two-colour laser field can increase the ionization probability of higher charge state.