Noise in the wire: The real impact of wire resistance for the Johnson(-like) noise based secure communicator

We re-evaluate the impact of wire resistance on the noise voltage and current in the Johnson(-like) noise based secure communicator, correcting the result presented in [J. Scheuer, A. Yariv, Phys. Lett. A 359 (2006) 737]. The analysis shown here is based on the fluctuation-dissipation and the linear response theorems. The results indicate that the impact of wire resistance in practical communicators is significantly lower than the previous estimation.     

融入凝聚态世界的时间晶体

<正>普通晶体破缺了空间平移对称性,而时间晶体则破缺了时间平移对称性。探索四维时空中晶体行为是一个崭新的研究方向,将会带来创新性的凝聚态器件和应用。在计算机芯片或是超导器件的内部,无数的电子在排列成晶格的离子间穿梭而过。这样的景象会不会在时间而不是空间中周而复始呢?传统的凝聚态器件或是电子元件会不会有四维时空中的新奇应用呢?麻省理工学院的诺贝尔物理学奖得主维尔切克(Frank Wilczek)在2012年题为《量子时间晶体》的开创性工作中提出了一个问题:时间平移对称性,也就是说不同时刻的     

Empirical extraction of mechanisms underlying real world network generation

The generation mechanisms of real world networks have been described using multiple models. The mathematical features of these models are usually extrapolated from statistical properties of a snapshot of these networks. We here propose an alternative method based on direct measurement of a sequence of consecutive snapshots to uncover the dynamics underlying real world generation. We assume that the probability of adding a node or an edge depends only on local features surrounding the newly added node/edge, and directly measure the contribution of these features to the node/edge addition probability. These measurements are performed using newly defined N-node local structures. Each N-node local structure represents the configuration of edges surrounding a newly added edge. The N-node local structure measurements reproduce for some networks the now classical addition of edges between high degree node mechanisms. It also provides quantitative estimates of more complex mechanisms driving other networks’ evolution, such as the effect of common first and second neighbors. This new methodology reveals the relative importance of different generation mechanisms. We show, for example, that the main mechanism driving hyperlink addition between two websites is the existence of a third website linking to both the source and the target of the new hyperlink.     

Dynamic modeling and simulation of a real world billiard

Gravitational billiards provide an experimentally accessible arena for testing formulations of nonlinear dynamics. We present a mathematical model that captures the essential dynamics required for describing the motion of a realistic billiard for arbitrary boundaries. Simulations of the model are applied to parabolic, wedge and hyperbolic billiards that are driven sinusoidally. Direct comparisons are made between the model?s predictions and previously published experimental data. It is shown that the data can be successfully modeled with a simple set of parameters without an assumption of exotic energy dependence.     

Ionization effects of the heavy components of cosmic radiation in protected chips

Radiation effects leading to degradation and failures in the operation of electronic equipment on board a space ship are of increasing concern in connection with the constantly decreasing sizes and increasing density of modern onboard microelectronics elements. The propagation of the energetic heavy ions of galactic cosmic rays (GCR) through a multi-layer structure (an integrated-circuit prototype) is discussed in the paper. The amount of electron-hole pairs induced by an ion in the sensitive area of a transistor has been estimated with consideration for energy losses in the chip body as well as in the protective oxide layers, contacts, and metallized layers. Calculation of the energy of various particles initiating the generation of a charge potentially capable to induce a single failure of onboard electronics has been carried out. The existence of a spatial region from which heavy fragments of a nuclear reaction, with a kinetic energy sufficient enough to induce a charge above the critical one, can penetrate into the gate region of a transistor has been demonstrated.     

Dynamics of surface migration in the weak corrugation regime

We report a systematic study for metal-on-metal surface migration in the weak corrugation regime, i.e., with migration barriers falling below approximately 100 meV. The migration characteristics are elucidated by variable-temperature scanning tunneling microscopy observations in the 50-200 K temperature range, which are analyzed by means of nucleation theory. The results demonstrate that, upon entering the weak corrugation regime, the dynamics of the systems are characterized by increasingly reduced effective preexponential factors, while Arrhenius behavior prevails.     

Polaronic effects in asymmetric quantum wire: An all-coupling variational approach

An all-coupling variational calculation based on Lee-Low-Pines-Huybrechts (LLPH) theory is performed to study the ground state and the first excited state in an asymmetric polar semiconductor quantum wire that is valid for the entire range of the electron-phonon coupling constant and arbitrary confinement length. It is shown that the polaronic effects are very important and size dependent, if the effective width of the wire is reduced below a certain length scale. It is also shown that asymmetry in a quantum wire can be used as an extra parameter to increase the stability of the polaron. Finally the theory is applied to a realistic CdS quantum wire.     

Mass-asymmetry effects in coupled electron-hole quantum wire system

The effect of mass-asymmetry on the ground-state of coupledelectron-hole quantum wire system is investigated within thequantum version of the self-consistent mean-field approximationof Singwi, Tosi, Land, and Sjölander. The pair-correlationfunctions, static density susceptibility, and correlation energy arecalculated over a range of wire parameters.We find that themass-asymmetry affects appreciably both the intra- and inter-wire correlations,which in turn bring in a marked change in the e-h ground-state.Below a critical density, the e-h correlations now favor theliquid-Wigner crystal phase transition at a sufficiently large wirespacing. This result is in striking difference with the correspondingstudy on the mass-symmetric e-h wire model since here transition to theWigner crystal phase occurs in the adequately closeproximity of two wires at a much lower density, and there also occurs acrossover from Wigner to a charge-density-wave phase at relatively higherdensities. We find that for a GaAsbased e-h wire the critical density for Wignercrystallization is enhanced by a factor of about 2.6.As an important result, our theory captures nicely the recentexperimental observation of Wigner crystallization in anun-equal density GaAs based e-h wire by Steinberg et al.[Phys. Rev. B 73, 113307 (2006)].     

Theory of exciton effects in the high-field magnetoabsorption of real semiconductors

Direct exciton states of cubic semiconductors in a high magnetic field are investigated taking into full account the degeneracy and anisotropy of the valence bands. The adiabatic method is used to decouple the components of the motion parallel and perpendicular to the magnetic field. One-dimensional Hamiltonians are obtained analytically for the various exciton states and selection rules for optical transitions are discussed. Accurate numerical values of the energy levels are given for H parallel to the (110) direction. The results obtained provide the first quantitative interpretation of the fine structure observed in high resolution measurements of magnetoabsorption in Ge.     

Atom pairs in the micromaser

Although in standard micromaser experiments the collective events, in which two or more atoms are inside the resonator at one time, are very rare, they may cause dramatic effects nevertheless. We find in particular that the so-called “trapped vacuum state” (in which single atoms would undergo a complete Rabi cycle while traversing the cavity and emerge without having emitted a photon) is destroyed even when more than 99% of the atoms participate in one-atom events.     

Exchange and correlation effects in a semiconductor quantum-well wire

The exchange and correlation effects of a quasi-one-dimensional electron gas are investigated by using the self-consistent-field approximation theory proposed by Singwi, Tosi, Land and Sjölander for the response function of the electron system. The present results are applied to GaAs-GaAlAs rectangular quantum-well-wires with the appropriate form factors that take into account the influence of the finite width of the electron layer. The plasmon dispersion relation and structure factor are calculated as a function of electron density and thickness of the wire. Results for the total energy per electron including kinetic, exchange and correlation energies and electron effective mass are presented. The Hartree-Fock and the random-phase approximation (RPA) results are also presented for comparison. We have found that exchange and correlation effects are more evident in wires of reduced dimensions.     

Scale free effects in world currency exchange network

A large collection of daily time series for 60 world currencies' exchange rates is considered. The correlation matrices are calculated and the corresponding Minimal Spanning Tree (MST) graphs are constructed for each of those currencies used as reference for the remaining ones. It is shown that multiplicity of the MST graphs' nodes to a good approximation develops a power like, scale free distribution with the scaling exponent similar as for several other complex systems studied so far. Furthermore, quantitative arguments in favor of the hierarchical organization of the world currency exchange network are provided by relating the structure of the above MST graphs and their scaling exponents to those that are derived from an exactly solvable hierarchical network model. A special status of the USD during the period considered can be attributed to some departures of the MST features, when this currency (or some other tied to it) is used as reference, from characteristics typical to such a hierarchical clustering of nodes towards those that correspond to the random graphs. Even though in general the basic structure of the MST is robust with respect to changing the reference currency some trace of a systematic transition from somewhat dispersed – like the USD case – towards more compact MST topology can be observed when correlations increase.     

Optical coherent transient effects in a magnetized semiconductor quantum wire

Effects of an external magnetic field on free induction decay (FID) and the Stark effect in GaAs/GaAlAs quantum wires have been investigated analytically. Our results show that both FID and the Stark effect become enhanced due to the presence of a magnetic field. We have also seen that the magnetic field plays an important role in wider wires while in thinner wires, the geometric confinement dominates over the magnetic effects. The results are found to be in good qualitative agreement with that available in the literature.