Dynamics of solitons in Bose-Einstein condensate with time-dependent atomic scattering length

The evolution of solitons in Bose--Einstein condensates (BECs) with time-dependent atomic scattering length in an expulsive parabolic potential is studied. Based on the extended hyperbolic function method, we successfully obtain the bright and dark soliton solutions. In addition, some new soliton solutions in this model are found. The results in this paper include some in the literature ({\em Phys. Rev. Lett.} {\bf 94} (2005) 050402 and {\em Chin. Phys. Lett.} {\bf 22} (2005) 1855).     

Experimental observation of partial amplitude death in coupled chaotic oscillators

The dynamics of coupled Lorenz circuits is investigated experimentally. The partial amplitude death reported in {\em Phys. Rev.} E {\bf 72}, 057201 (2005) is verified by physical experiments with electronic circuits. With the increase of coupling constant, the coupled circuits undergo the transition from the breakdown of both the reflection symmetry and the translational symmetry to the partial amplitude death. Its stability is also confirmed by analysing the effects of noise.     

Quantum circuits for realizing deterministic and exact teleportation via two partially entangled pairs of particles

Deterministic and exact teleportation can be achieved via two partially entangled pairs of particles [Gu Y J 2006 {\em Opt. Comm.} {\bf 259} 385]. The key point of the protocol is a generalized measurement described by a positive operator-valued measure, which can be realized by performing a unitary operation in the extended space and a conventional Von Neumann orthogonal measurement. By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the teleportation. Our method for constructing quantum circuits differs from the usual methods based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements.     

Generation of four-particle GHZ states in bimodal cavity QED

We propose a scheme for preparing four-particle Greenberger--Horne--Zeilinger states using two identical bimodal cavities, each supports two modes with different frequencies. This scheme is an alternative to another published work [Christopher C Gerry 1996 {\it Phys. Rev.} A {\bf 53} 4591]. Comparisons between them are discussed. The fidelity and the probability of success influenced by cavity decay for the generated states are also considered.     

Deterministic quantum teleportation and information splitting via a peculiar W-class state

In the paper ({\em Phys. Rev.} 2006 A {\bf 74} 062320) Agrawal {\em et al}. have introduced a kind of W-class state which can be used for the quantum teleportation of single-particle state via a three-particle von Neumann measurement, and they thought that the state could not be used to teleport an unknown state by making two-particle and one-particle measurements. Here we reconsider the features of the W-class state and the quantum teleportation process via the W-class state. We show that, by introducing a unitary operation, the quantum teleportation can be achieved deterministically by making two-particle and one-particle measurements. In addition, our protocol is extended to the process of teleporting two-particle state and splitting information.     

Dynamical Breaking of Generalized Yang-Mills Theory

The dynamical breaking of a generalized Yang-Mills theory is discussed. It is shown, in terms of the Nambu Jona-Lasinio mechanism, that the gauge symmetry breaking can be realized dynamically in the generalized Yang-Mills theory. The combination of the generalized Yang-Mills theory and the NJL mechanism provides a way to overcome the difficulties related to the Higgs field and the Higgs mechanism in the usual spontaneous symmetry breaking theory.     

Entanglement in a generalized Jaynes--Cummings model

We investigate the pairwise entanglement and global entanglement in a generalized Jaynes--Cummings model, which can be used to realize Greenberger--Horne--Zeilinger (GHZ) entangled state (Zheng S B 2001 {\it Phys. Rev. Lett.} {\bf 87} 230404). Our results show that the W-type entangled states cannot be generated based on the model. The dependences of entanglement on Rabi frequency $\lambda$ and dipole--dipole coupling strength ${\it \Omega}$ are given. It is found that there exists the quantum phase transition when $\lambda={\it \Omega}$. For typical experimental data, the critical temperature for pairwise entanglement is on the order of $10^{-6}$\,K. Based on these results, two strategies that overcome decoherence are proposed.     

MHD Flow Towards a Permeable Surface with Prescribed Wall Heat Flux

The steady magnetohydrodynamic （MHD） mixed convection flow towards a vertical permeable surface with prescribed heat flux is investigated. The governing partial differential equations are transformed into a system of ordinary differential equations, which is then solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analysed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions exist for the assisting flow, besides the solutions usually reported in the literature for the opposing flow.     

Effects of the number of on-rampson the ring traffic flow

Since ramp is an important composition of traffic system and there often exist multi ramps in a traffic system, the number of ramps can have great effects on main road traffic and produce some complex phenomena. In this paper, we employ the model presented by Tang \textit{et al}. [2009 {\em Communications in Theoretical Physics} {\bf 51}({1}) 71] to further study the effects of the number of on-ramps on the stability of traffic flow on a ring road. The numerical results show that this model can reproduce some complex traffic phenomena resulting from multi on-ramps on the ring road and the effects of the number of on-ramps on traffic flow, but the phenomena and the effects are both related to the initial density of the main road.     

Distillation of bi-partite entanglement from W state with cavity QED

Following the theoretical protocol described by Fortescue and Lo [Fortescue B and Lo H K 2007 Phys. Rev. Lett. 98 2605011, we present a scheme in which one can distill maximally entangled bi-partite states from a tri-partite W state with cavity QED. Our scheme enables the concrete physical system to realize its protocol. In our scheme, the rate distillation also asymptotically approaches one. Based on the present cavity QED techniques, we discuss the experimental feasibility.     

Perturbation to Lie symmetry and another type of Hojman adiabatic invariants for Birkhoffian systems

The perturbation to Lie symmetry and another type of Hojman adiabatic invariants induced from the perturbation to Lie symmetry for Birkhoffian systems are studied. The exact invariants of Lie symmetry for the system without perturbation are given. Based on the concept of adiabatic invariant, the perturbation to Lie symmetry is discussed and another new type of Hojman adiabatic invariants that have the different form from that in [Acta Phys. Sin. 55 3833] for the perturbed system are obtained.     

Theoretical study on decay of the 4d core-excited states of Cs III

In a recent XUV photoabsorption spectrum of Cs Ⅲ ions by Cummings and O＇Sullivan [2001 J. Phys. B 34 199], rather large linewidths were found for the 4d^95s^25p^6 - 4d^105s^25p^5 transition which are quite in disagreement with corresponding quasi-relativistic multiconfiguration Hartree Fock （MCHF） calculation. In the present work, a detailed multiconfiguration Dirac-Fock study has been carried out to explore this discrepancy. Owing to the detailed consideration of electron correlation effects, some ‘forbidden＇ Auger decay channels, such as 4d^105s^25p^35d and 4d^105s^05p^6, would become ‘open＇. As a result, remarkable improvement of the linewidths has been obtained in our calculation. Furthermore, the theoretical Auger spectrum of the 4d^ 95s^25p^6 core-excited states of Cs Ⅲ ions is Riven in the present work.     

Kinetic Ising model in a time-dependent oscillating external magnetic field: effective-field theory

Recently,Shi et al.[2008 Phys.Lett.A 372 5922] have studied the dynamical response of the kinetic Ising model in the presence of a sinusoidal oscillating field and presented the dynamic phase diagrams by using an effective-field theory(EFT) and a mean-field theory(MFT).The MFT results are in conflict with those of the earlier work of Tom’e and de Oliveira,[1990 Phys.Rev.A 41 4251].We calculate the dynamic phase diagrams and find that our results are similar to those of the earlier work of Tom’e and de Oliveira;hence the dynamic phase diagrams calculated by Shi et al.are incomplete within both theories,except the low values of frequencies for the MFT calculation.We also investigate the influence of external field frequency(ω) and static external field amplitude(h0) for both MFT and EFT calculations.We find that the behaviour of the system strongly depends on the values of ω and h0.     

Molecular dynamics study of the ternary compound Li3AlB2O6

A new compound with the stone cheinical composition as Li3AlB2O6 but with a different x-ray powder diffraction pattern as reported before was synthesized and studied experimentally by M. He, Chen X Let al （J. Solid State Chem. 163, 369 （2002））, but there lacks first principles study on the structure of it. Using conjugant gradient （CG） molecule dynamics （MD） simulation with a full relaxation of the atomic positions and of the shape and size of the cell, the structure of Li3AlB2O6 is studied from first principles. For the density functional, the local density approximation （LDA） and the generalized gradient approximation （GGA） forms are used respectively. Both the LDA and GGA results support the experimental structure of M. He et al. The result of MD simulation using GGA agrees with the experimental result much better. The energy bands are also studied, the band gap given by LDA and GGA are 5.65 eV, 5.34eV, respectively.     

Magnetic field induced phase branches of the superconducting transition in two-dimensional square π-loop arrays

Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square $\pi $-loop arrays given by Li \textit{et al} [2007 {\em Chin. Phys.} {\bf 16} 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux $\phi_{\e}$ through each loop and monotonically on the screen parameter $\beta $ of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the $\pi $-loop arrays is also discussed.