Table of contents

The effects of decoherence on the transfer and storage of coherent quantum states in hybrid systems are studied within the Caldeira-Leggett approach. In general, we find that a high transfer fidelity can be achieved even if the decoherence time is less than an order of magnitude larger than the transfer time, which is approximately half a Rabi period and determined by the qubit-qubit coupling strength. Finally, we apply our results to assess the feasibility of a hybrid quantum memory system, comprised of the hyperfine qubit states of an ultracold atomic Bose-Einstein condensate and the flux qubit of a SQUID.

We study a lattice model of two perpendicular intersecting flows of pedestrians represented by hard-core particles of two types, eastbound ("${\cal E}$") and northbound ("${\cal N}$"). Each flow takes place on a strip of width M so that the intersection is an M × M square lattice. In experiment and simulation there occurs on this square spontaneous formation of a diagonal pattern of alternating ${\cal E}$ and ${\cal N}$ particles. We show that this pattern formation may be understood in terms of a linear instability of the corresponding mean-field equations. A refined investigation reveals that the pattern actually consists of chevrons rather than straight diagonals. We explain this effect as the consequence of the existence of a nonlinear mode sustained by the interaction between the two types of particles.

In this letter, we find how the frequency of an oscillation determines the exact form of the control for suppressing the oscillation through feedback controls with time delays. These results are based on necessary and sufficient conditions we analytically established for the stability of a dynamical system with feedback control and time delays. We also interpret how these conditions change as the time delay either is equal to zero or becomes larger appropriately. All the analytical and numerical results are illustrated by suppressing the oscillations of the FitzHugh-Nagumo model and by the oscillation death and synchronization phenomena observed in a complex dynamical network with time-delayed couplings. Our findings could be potentially useful for modulating oscillations through proper control devices in various fields.

A random walk consisting of a run phase at constant speed interrupted by tumble events is analyzed and analytically solved for arbitrary time distributions. A general expression is given for the Laplace-Fourier transform of the probability density function and for the mean square displacement averaging over initial conditions. Run-and-tumble bacteria and Lévy walks are considered as particular cases. The effects of an underlying Brownian noise are also discussed. Derived expressions can be used for a direct comparison with experimentally measured quantities.

The origin of the quantum Zeno paradox is critically re-evaluated. It is demonstrated, that the observation of expectation values, in particular of reduced decay constants, cannot qualify as the proof of a quantum Zeno effect. Rather, the detection of the transition times of individual quantum objects provides necessary and sufficient evidence.

The optical medium analogy of a radiation field generated by either an exact gravitational plane wave or an exact electromagnetic wave in the framework of general relativity is developed. The equivalent medium of the associated background field is inhomogeneous and anisotropic in the former case, whereas it is inhomogeneous but isotropic in the latter. The features of light scattering are investigated by assuming the interaction region to be sandwiched between two flat spacetime regions, where light rays propagate along straight lines. Standard tools of ordinary wave optics are used to study the deflection of photon paths due to the interaction with the radiation fields, allowing for a comparison between the optical properties of the equivalent media associated with the different background fields.

The asymptotic safety scenario of gravity conjectures that i) the quantum field theory of gravity exists thanks to the presence of a non-trivial ultraviolet fixed point of the renormalization group, and that ii) the fixed point has only a finite number of relevant perturbations, i.e., a finite number of UV-stable directions (or, in other words, a finite number of free parameters to be fixed experimentally). Within the f(R) approximation of the functional renormalization group equation of gravity, we show that assuming the first half of the conjecture to be true, the remaining half follows from general arguments, that is, we show that assuming the existence of a non-trivial fixed point, the fact that the number of relevant directions is finite is a general consequence of the structure of the equations.

In this letter we consider a specific model of braneworld with nonstandard dynamics diffused in the literature, specifically we focus our attention on the matter energy density, the energy of system, the Ricci scalar and the thin-brane limit. As the model is classically stable and capable of localize gravity, as a natural extension we address the issue of fermion localization of fermions on a thick brane constructed out from one scalar field with nonstandard kinetic terms coupled with gravity. The contribution of the nonstandard kinetic terms to the problem of fermion localization is analyzed. It is found that the simplest Yukawa coupling $\eta \bar {\Psi }\phi \Psi$ supports the localization of fermions on the thick brane. It is shown that the zero mode for left-handed fermions can be localized on the thick brane depending on the values for the coupling constant η.

We analyze the force on a point charge moving at relativistic speeds parallel to the surface of a uniaxial dielectric. Two cases are examined: a lossless dielectric with no dispersion and a dielectric with a plasma-type response. The treatment focuses on the peculiarities of the strength and direction of the interaction force as compared to the isotropic case. We show that a plasma-type dielectric can, under specific conditions, repel the point charge.

We show an image distance shift effect of the metal superlens, which is that in the case in which the pattern of a mask acting as an object and the distance from the mask to a given metal superlens are fixed, the image distance of the given metal superlens is shifted to larger values with decreasing the thickness of the mask or increasing the dielectric constant of the filling material in the slits of the mask. A possible explanation of this effect is proposed. Furthermore, simulation results show that, by using the reported effect, the performance of the metal superlens lithography technique assisted by a plasmonic mirror can be significantly improved.

We numerically investigate the optical bistability with highly confined surface plasmon polaritons (SPPs) modes excitation in a metal-nonlinear dielectric multilayer nanostructure. We find that the field distribution forms a standing wave through the excitation of coupled SPPs in nanomultilayers caused by the Fabry-Perot interferometer. In addition, the average field amplitude is increased by a factor of ∼20.6 compared to that of the incident beam. A very low bistability threshold of 2.75 MW/cm² is obtained with a fundamental SPPs mode excitation at the telecommunication wavelength of 1550 nm.

In this letter, we present the first experimental study of bridge structures in three-dimensional dry granular packings. When bridges are small, they are predominantly "linear", and have an exponential size distribution. Larger, predominantly "complex" bridges, are confirmed to follow a power-law size distribution. Our experiments, which use X-ray tomography, are in good agreement with the simulations presented here, for the distribution of sizes, end-to-end lengths, base extensions and orientations of predominantly linear bridges. Quantitative differences between the present experiment and earlier simulations suggest that packing fraction is an important determinant of bridge structure.

This paper describes the fabrication procedure and optical characterization of ferroelectric liquid-crystal (FLC) gratings based on photo-alignment. The fabrication procedure includes only one side photo-alignment substrate, while the other substrate does not have any alignment layer. Both 1D and 2D gratings have been fabricated. The proposed diffraction element shows high diffraction efficiency ∼ 65% and fast response time of 50 μs, which is much faster than the existing technologies. Such gratings can be operated with high frequency of around 2 kHz at the electric field of 6.67 V/μm. Moreover, the proposed grating can be erased and rewritten optically for different grating vector in simple steps. Therefore, with these advance features, such gratings have high potential to be applied in verity of devices and for the improvement of some important existing devices.

Through a systematic experimental investigation of the behavior of falling granular jets under the action of gravity for different particle sizes, funnel diameters and ambient air pressures, necessary conditions to obtain incompressible granular jets are identified. A transition from compressible (characterized by a significant density decrease along the propagation) to incompressible granular jets (characterized by a constant density) is observed. This transition depends solely on the aspect ratio between the diameter of the particles and the diameter of the funnel. Surprisingly, the incompressible liquid-like behavior observed here seems to find its origin in the balance between the heat flux and the dissipation in the funnel independently of the ambient fluid pressure. A simple granular hydrodynamic model provides a good description of the transition.

Molecular-dynamics simulations have been performed to investigate metallic-nanowire (NW) induced spontaneous scrolling of single-layered graphene (SLG) nanostructures. This unique behavior is attributed to the van der Waals attraction between the SLG and NW and the π-π stacking effect between SLG layers. The scrolling velocity shows a nonlinear dependence on time. Such self-scrolling of SLG is hindered by the surface roughness and especially the oxygen concentration of NW. SLGs with arbitrary sizes and shapes can wrap onto NW to form various configurations. The proposed discoveries eventually provide a powerful way to fabricate nanoscale composite materials and devices and tune their properties.

Optical absorption induced by swift heavy-ion irradiations in AlN was studied in situ at 15 K. Detailed analysis of the influence of both electronic and nuclear stopping power indicates that the electronic energy loss does not create the point defects inducing the observed absorption band at 4.7 eV. Elastic displacements are required. Nevertheless, an unexpected non-linear enhancement is induced by the electronic energy loss. The intensity of the synergy between electronic excitations and elastic collisions increases markedly with the electronic stopping power. For the heaviest projectiles, the enhancement of the color center creation yield amounts to two orders of magnitude.

Charge carriers in single and multilayered graphene systems behave as chiral particles due to the particular lattice symmetry of the crystal. We show that the interplay between the meta-material properties of graphene multilayers and the pseudospinorial properties of the charge carriers result in the occurrence of Klein and anti-Klein tunneling for rhombohedral stacked multilayers. We derive an algebraic formula predicting the angles at which these phenomena occur and support this with numerical calculations for systems up to four layers. We present a decomposition of an arbitrarily stacked multilayer into pseudospin doublets that have the same properties as rhombohedral systems with a lower number of layers.

Multiferroic Bi_1−xCa_xFeO_3−x/2 (0.10 ⩽ x ⩽ 0.50) materials have been synthesized via a high-temperature sintering method. The structural properties have been studied using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The EELS measurements reveal that the oxidation state of Fe ions in these compounds is Fe⁺³, and oxygen vacancies are created as Ca substitutions for Bi. A series of superstructure modulations appear along the a-axis direction, and their wavelength can be written as L = na (n = 4, 5, 6 and 7) depending on the Ca contents. Based on our structural analysis, we interpret these superstructures in terms of oxygen-vacancy ordering associated with local structural distortions.

Recently fabricated single-crystalline atomically flat metallic nanofilms are in fact quantum-engineered multiband superconductors. Here the multiband structure is dictated by the nanofilm thickness through the size quantization of the electron motion perpendicular to the nanofilm. This opens the unique possibility to explore superconductivity in well-controlled multi-band systems. However, a serious obstacle is the absence of a convenient and manageable theoretical tool to access new physical phenomena in such quasi–two-dimensional systems, including interplay of quantum confinement and fluctuations. Here we cover this gap and construct the appropriate multiband Ginzburg-Landau functional for nano-thin superconductors.

Vortex states of two-band superconductors are investigated based on the microscopic Ginzburg-Landau model. We show that the nonlocal interband coupling can lead to the breaking of translation symmetry and the axial rotation symmetry of the conventional Abrikosov vortex states, resulting in a novel vortex structure comprising a mixture of triangle and square-like vortex lattices that have no counterparts in the single-band superconductors. Half-quantized vortices and stable vortex-antivortex pairs are found. These results may relate to the experimental observations of anomalous vortex structures in the two-band magnesium diboride superconductor.

The phenomenon of synchronous firings is investigated in excitable small-world networks (ESWNs) of 2D lattices. Two sharply different types of patterns, wavelet turbulence (WT) patterns and synchronous firing (SF) patterns, and the associated transitions and hysteresis are found in wide parameter regions and in different excitable models. The WT state is maintained by wavelet defects while the SF state is due to iterative excitations between majority nodes and minority nodes where defects do not play essential roles. Moreover, a dominant phase-advanced driving method is applied to explain how self-sustained SFs can be maintained in ESWN and why SF and WT states show distinctive characteristic features. Since excitability of node and small-world network structure are two essential ingredients of some neural subsystems and SFs are important for many neural functions, the results in this paper are thus expected to be instructive for understanding the dynamics of some neural networks.

We study the optimal routing on multilayered communication networks, which are composed of two layers of subnetworks. One is a wireless network, and the other is a wired network. We develop a simple recurrent algorithm to find an optimal routing on this kind of multilayered networks, where the single-channel transmission mode and the multichannel transmission mode used on the wireless subnetwork are considered, respectively. Compared with the performance of the shortest path algorithm, our algorithm can significantly enhance the transport capacity. We show that our methods proposed in this letter could take advantage of the coupling of the two layers to the most extent, so that the wireless subnetwork could sufficiently utilize the wired subnetwork for transportation.

Sodium sulfate is recognized as a salt with probably the most damaging capabilities when crystallizing in porous media. The three main crystalline phases which can be formed are thenardite (Na₂SO₄, anhydrous salt), decahydrate (Na₂SO₄·10H₂O) and the thermodynamically metastable heptahydrate (Na₂SO₄·7H₂O). In this study, using a setup in which nuclear magnetic resonance was combined with a digital microscope, we have investigated crystallization by the drying of sodium sulfate droplets on hydrophilic/hydrophobic surfaces in order to see, which crystalline phase is formed.

The dynamics and rheology of suspensions of fluid vesicles or red blood cells is investigated by a combination of molecular dynamics and mesoscale hydrodynamics simulations in two dimensions. The vesicle suspension is confined between two no-slip walls, which are driven externally to generate a shear flow with shear rate $\dot \gamma$. The flow behavior is studied as a function of $\dot \gamma$, the volume fraction of vesicles, and the viscosity contrast between inside and outside fluids. Results are obtained for the encounter and interactions of two vesicles, the intrinsic viscosity of the suspension, and the cell-free layer near the walls.

Mapping a planar conductor with arbitrary electronic band structure (e.g., linear or parabolic) to a slab of bulk medium exhibiting the same optical responses, we formulated an equivalent-medium approach to study the optical properties of metamaterials (MTMs) made by patterning such a planar conductor, particularly for the graphene system. The theory was applied to study various graphene-based MTMs, with calculation results in one particular system (with no adjustable parameters) agreeing well with available experiments.

A non-extensive statistical physics approach is tested for the first time in a planetary scale, for the fault length distribution in Mars estimated a non-extensive q-parameter equal to 1.277 for normal faults and 1.114 for thrust ones. The latter support the conclusion that the fault systems in Mars are subadditive ones in agreement with recent observations for faults in Earth and Valles Marineris extensional province, Mars. In addition, an analysis of the global Mars fault system as a mixed one, consisted of the normal and thrust subsystems with different q-parameters is presented, leading to q = 1.22.

Many real-world complex systems are adequately represented by networks of interacting or interdependent networks. Additionally, it is often reasonable to take into account node weights such as surface area in climate networks, volume in brain networks, or economic capacity in trade networks to reflect the varying size or importance of subsystems. Combining both ideas, we derive a novel class of statistical measures for analysing the structure of networks of interacting networks with heterogeneous node weights. Using a prototypical spatial network model, we show that the newly introduced node-weighted interacting network measures provide an improved representation of the underlying system's properties as compared to their unweighted analogues. We apply our method to study the complex network structure of cross-boundary trade between European Union (EU) and non-EU countries finding that it provides relevant information on trade balance and economic robustness.

Large-scale ab initio molecular-dynamics simulations have been carried out to compute, at human-body temperature, the vibrational modes and lifetimes of pure and hydrated dipalmitoylphosphatidylcholine (DPPC) lipids. The projected atomic vibrations calculated from the spectral energy density are used to compute the vibrational modes and the lifetimes. All the normal modes of the pure and hydrated DPPC and their frequencies are identified. The computed lifetimes incorporate the full anharmonicity of the atomic interactions. The vibrational modes of the water molecules close to the head group of DPPC are active (possess large projected spectrum amplitudes) in the frequency range 0.5–55 THz, with a peak at 2.80 THz in the energy spectrum. The computed lifetimes for the high-frequency modes agree well with the recent data measured at room temperature where high-order phonon scattering is not negligible. The computed lifetimes of the low-frequency modes can be tested using the current experimental capabilities. Moreover, the approach may be applied to other lipids and biomolecules, in order to predict their vibrational dispersion relations, and to study the dynamics of vibrational energy transfer.

Cascading failures of loads in isolated networks under random failures or intentional attacks have been studied in the past decade. The corresponding results for interconnected networks remain missing. In this paper we extend the cascading failure model used in isolated networks to the case of interconnected networks, and study cascades of failures in a data-packet transport scenario. We find that for sparse coupling, enhancing the coupling probability can make interconnected networks more robust against intentional attacks, but keeping increasing the coupling probability has the opposite effect for dense coupling. Additionally, the optimal coupling probability is largely affected by the coupling preference. Finally, assortative coupling is more helpful to resist the cascades compared to disassortative or random coupling. These results can be useful for the design and optimization of interconnected networks such as communication networks, power grids and transportation systems.

The physics of the breakdown of a green wave (GW) in a city is revealed. We have found that there are two regions of flow rates in the GW within which the GW breakdown is possible. In the region of larger flow rates bounded by the maximum capacity and threshold flow rate, a time-delayed spontaneous GW breakdown occurs with some probability during a given observation time. In the region of smaller flow rates bounded by the threshold flow rate and minimum capacity, only an induced GW breakdown is possible. The GW breakdown can be simulated with traffic flow models in the context of either three-phase or two-phase theories. However, in three-phase models the spontaneous GW breakdown is initiated by the emergence of a moving synchronized flow pattern (MSP); the MSP results from an initial speed disturbance at the beginning of the GW. In contrast, in two-phase models no MSPs can occur, therefore, considerably heavier conditions for both spontaneous and induced GW breakdowns are found.

We present a density-functional–based closure of the pair Smoluchowski equation for Brownian particles under shear flow. Given an equilibrium free-energy functional as input, the theory provides first-principles predictions for the flow-distorted pair correlation function and associated rheological quantities over a wide range of volume fractions and flow rates. Taking two-dimensional hard disks under shear flow as an illustrative model, we calculate the pair correlation function, viscosity and normal-stress difference under both steady and start-up shear.

Species diversity in ecosystems is often accompanied by the self-organisation of the population into fascinating spatio-temporal patterns. Here, we consider a two-dimensional three-species population model and study the spiralling patterns arising from the combined effects of generic cyclic dominance, mutation, pair-exchange and hopping of the individuals. The dynamics is characterised by nonlinear mobility and a Hopf bifurcation around which the system's phase diagram is inferred from the underlying complex Ginzburg-Landau equation derived using a perturbative multiscale expansion. While the dynamics is generally characterised by spiralling patterns, we show that spiral waves are stable in only one of the four phases. Furthermore, we characterise a phase where nonlinearity leads to the annihilation of spirals and to the spatially uniform dominance of each species in turn. Away from the Hopf bifurcation, when the coexistence fixed point is unstable, the spiralling patterns are also affected by nonlinear diffusion.

In the model of holographic dark energy, there is a notorious problem of circular reasoning between the introduction of future event horizon and the accelerating expansion of the universe. We examine the problem after dividing it into two parts, the causality problem of the equation of motion and the circular logic on the use of the future event horizon. We specify and isolate the root of the two problems as a boundary condition from the causal equation of motion, which can be determined from the initial data of the universe. We show that the causality will be kept if we define it based on our recognizability and the circular-logic problem can be reduced to imposing an initial condition. We additionally find that the model constant of the holographic dark energy is close to unity from the present data of the universe.