Modern Physics Letters B

Feynman's "no-node" theorem states that the conventional many-body ground state wavefunctions of bosons in the coordinate representation are positive definite. This implies that time-reversal symmetry cannot be spontaneously broken. In this article, we review our progress in studying a class of new states of unconventional Bose–Einstein condensations beyond this paradigm. These states can either be the long-lived metastable states of ultracold bosons in high orbital bands in optical lattices as a result of the "orbital Hund's rule" interaction, or the ground states of spinful bosons with spin-orbit coupling linearly dependent on momentum. In both cases, Feynman's argument does not apply. The resultant many-body wavefunctions are complex-valued and thus break time-reversal symmetry spontaneously. Exotic phenomena in these states include the Bose–Einstein condensation at nonzero momentum, the ordering of orbital angular momentum moments, the half-quantum vortex, and the spin texture of skyrmions.

We study quantum phases of ultracold bosonic atoms in a two-dimensional optical superlattice. The extended Bose–Hubbard model derived from the system of ultracold bosonic atoms in an optical superlattice is solved numerically with the Gutzwiller approach. We find that the modulated superfluid (MS), Mott-insulator (MI) and density-wave (DW) phases appear in some regimes of parameters. The experimental detection of the first-order correlations and the second-order correlations of different quantum phases with time-of-flight and noise-correlation techniques is proposed.

In the letter, the global asymptotic stability of bidirectional associative memory (BAM) neural networks with delays is investigated. The delay is assumed to be time-varying and belongs to a given interval. A novel stability criterion for the stability is presented based on the Lyapunov method. The criterion is represented in terms of linear matrix inequality (LMI), which can be solved easily by various optimization algorithms. Two numerical examples are illustrated to show the effectiveness of our new result.

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for the scalable quantum information processor. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate, a combination of appropriate rf and DC potentials are applied to them for stable ion confinement, and the trap axes are located above the surface at a distance controlled by the electrodes' lateral extent and the substrate's height as discussed. The potential distributions are calculated using static electric field qualitatively. This architecture is conceptually simple and many current microfabrication techniques are feasible for the basic structure. It may provide a promising route for scalable quantum computers.

In this paper, a novel compact rat-race hybrid coupler incorporating square open-loop defected ground structures (SOL-DGSs) is designed and verified. As a new wave of microstrip electromagnetic bandgap element (MEBE) technology on ground plane, the bandgap characteristic of SOL-DGS is employed to reject the high-order harmonics without any additional filter and the excellent slow-wave effect of SOL-DGS is studied and utilized to reduce the circuit size in the design of the hybrid coupler. The measured insertion losses are 3.54 dB and 3.63 dB for two input ports. The isolation between port 1 and port 3 achieves around -30 dB. Furthermore, the proposed rat-race coupler successfully rejects the second, third, fourth and even fifth harmonic signals.

We studied numerically the influences of damping and temperature of medium on the properties of the soliton transported bio-energy in the α-helix protein molecules with three channels by using the dynamic equations in the improved Davydov theory and fourth-order Runge–Kutta method. From the simulation experiments, we see that the new solitons can move along the molecular chains without dispersion at a constant speed, in which the shape and energy of the soliton can remain in the cases of motion, whether short-time at T=0 or long time at T=300 K. In these motions, the soliton can travel over about 700 amino acid residues, thus its lifetime is, at least, 120 ps at 300 K. When the two solitons undergo a collision, they can also retain themselves forms to transport towards. These results are consistent with the analytic result obtained by quantum perturbed theory in this model. However, the amplitudes of the solitons depress along with increase of temperature of the medium, and it begins to disperse at 320 K. In the meanwhile, the damping of the medium can influence the states and properties of the soliton excited in α-helix protein molecules. The investigation indicates that the amplitude and propagated velocity of the soliton decrease, when the damping of medium increases. The soliton is dispersed at the large damping coefficient Γ=4 Γ₀ at 300 K. The results show that the soliton excited in the α-helix protein molecules with three channels is very robust against the damping and thermal perturbation of medium at biological temperature of 300 K. Thus we can conclude that the soliton can play important part in the bio-energy transport and the improved model is possibly a candidate for the mechanism of the energy transport in the α-helix proteins.

The dynamics of cathode spot movements on a three-dimensional carbon fiber reinforced carbon/carbon composite were investigated by a scanning electron microscope and a digital high-speed video camera. The results show that the motion direction of the cathode spots is parallel to the carbon fibers. The directed motion of the cathode spots is accompanied by the cycle of alternative splitting and extinguishment of cathode spots. The group of the cathode spots can split into two small groups when it moves far away from the ignition site. Within 40 μs, the two small groups completely depart each other. The splitting of the cathode spots group is caused by the current degradation. The former group continues to go forward, and the latter extinguishes within 40 μs. The transient and the average velocity of the "lead" spot are estimated to be 0.9–3.4 m/s and ~ 2.11 m/s, respectively. The diffusion constant of the cathode spot is (9.11±0.59) ×10^-5 m²/s.

Polycrystalline sample of NaCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis exhibits the orthorhombic crystal structure of the compound at room temperature. Detailed dielectric studies of NaCa₂Nb₅O₁₅ over a wide range of temperature (31–500°C) and frequency (10²–10⁶ Hz) did not show any dielectric anomaly (or ferroelectric phase transition) as observed in other members of the tungsten bronze structural family. However, the low loss tangent and dielectric constant increase with increasing temperature. Complex impedance and modulus plots (at different temperature and frequency) show the existence of non-Debye type of relaxation process in the compound. Complex modulus spectrum shows only grain contribution in the compound. Electric modulus analysis suggests that a possible hopping mechanism is evident for electrical transport processes in the system. Studies of AC conductivity with frequency suggest that the material obeys Jonscher's universal power law.