Search arXiv⌕ Search

arXiv subjects

Peng Zhang

Publications and source records attributed to Peng Zhang.

At least 811 records · Page 45Linked to original sources
arXiv2014

The effect of non-linear quantum electrodynamics on relativistic transparency and laser absorption in ultra-relativistic plasmas

With the aid of large-scale three-dimensional QED-PIC simulations, we describe a realistic experimental configuration to measure collective effects that couple strong field quantum electrodynamics to plasma kinetics. For two counter propagating lasers interacting with a foil at intensities exceeding $10^{22}$ Wcm$^{-2}$, a binary result occurs; when quantum effects are included, a foil that classically would effectively transmit the laser pulse becomes opaque. This is a dramatic change in plasma behavior, directly as a consequence of the coupling of radiation reaction and pair production to plasma dynamics.

physics.plasm-ph↗
arXiv2014

Characterizing and Modeling the Dynamics of Activity and Popularity

Social media, regarded as two-layer networks consisting of users and items, turn out to be the most important channels for access to massive information in the era of Web 2.0. The dynamics of human activity and item popularity is a crucial issue in social media networks. In this paper, by analyzing the growth of user activity and item popularity in four empirical social media networks, i.e., Amazon, Flickr, Delicious and Wikipedia, it is found that cross links between users and items are more likely to be created by active users and to be acquired by popular items, where user activity and item popularity are measured by the number of cross links associated with users and items. This indicates that users generally trace popular items, overall. However, it is found that the inactive users more severely trace popular items than the active users. Inspired by empirical analysis, we propose an evolving model for such networks, in which the evolution is driven only by two-step random walk. Numerical experiments verified that the model can qualitatively reproduce the distributions of user activity and item popularity observed in empirical networks. These results might shed light on the understandings of micro dynamics of activity and popularity in social media networks.

physics.soc-ph↗
arXiv2013

Path Integral and Asian Options

In this paper we analytically study the problem of pricing an arithmetically averaged Asian option in the path integral formalism. By a trick about the Dirac delta function, the measure of the path integral is defined by an effective action functional whose potential term is an exponential function. This path integral is evaluated by use of the Feynman-Kac theorem. After working out some auxiliary integrations involving Bessel and Whittaker functions, we arrive at the spectral expansion for the value of Asian options.

q-fin.PR↗
arXiv2013

Magneto--optical matter wave Bragg diffraction

We have performed a principle-proof-experiment of a magneto-optical diffraction (MOD) technique that requires no energy level splitting by homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this new MOD is that asynchronized switching of quadrupole trap and Ioffe trap in a quadrupole-Ioffe-configuration trap can generate a residual magnetic force to drive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matter-wave self-imaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction, and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer ($>110 \hbar k$) to a BEC using well-developed magnetic trapping techniques.

cond-mat.quant-gas↗
arXiv2013

Deterministic Sequences for Compressive MIMO Channel Estimation

This paper considers the problem of pilot design for compressive multiple-input multiple-output (MIMO) channel estimation. In particular, we are interested in estimating the channels for multiple transmitters simultaneously when the pilot sequences are shorter than the combined channels. Existing works on this topic demonstrated that tools from compressed sensing theory can yield accurate multichannel estimation provided that each pilot sequence is randomly generated. Here, we propose constructing the pilot sequence for each transmitter from a small set of deterministic sequences. We derive a theoretical lower bound on the length of the pilot sequences that guarantees the multichannel estimation with high probability. Simulation results are provided to demonstrate the performance of the proposed method.

cs.IT↗
arXiv2013

Beam steering and topological transformations driven by interactions between discrete vortex and fundamental solitons

We study coherent and incoherent interactions between discrete vortex and fundamental solitons in two-dimensional photonic lattices, presenting a new scheme for all-optical routings and topological transformations of vorticities. Due to the multi-lobe intensity and step-phase structure of the discrete vortex soliton, the coherent soliton-interactions allow both solitons to be steered into multiple different possible destination ports depending on the initial phase of the discrete fundamental soliton. We show that charge-flipping of phase singularities and orbital angular momentum transfer can occur during the coherent interactions between the two solitons. For incoherent interactions, by controlling the relative intensities of the two solitons, we reveal that soliton-steering can be realized by either attracting the discrete fundamental soliton to four ports or localizing the four-lobe discrete vortex soliton into a ring soliton.

physics.optics↗
arXiv2013

Constraining the Infrared Behavior of the Soft-Wall AdS/QCD Model

By requiring the correct Regge behavior in both meson and nucleon sectors, we determine the infrared asymptotic behavior of various background fields in the soft-wall AdS/QCD model, including the dilaton, the warp factor, and the scalar VEV. We then use a simple parametrization which smoothly connect these IR limits and their usual UV limits. The resulting spectrum is compared with experimental data, and the agreement between them is good.

hep-ph↗
arXiv2013

Engineered optical nonlinearities and enhanced light transmission in soft-matter systems with tunable polarizabilities

In this work, we demonstrate that the nonlinear response of certain soft-matter systems can be tailored at will by appropriately engineering their optical polarizability. In particular, we deliberately synthesize stable colloidal suspensions with negative polarizabilities, and observe for the first time robust propagation and enhanced transmission of self-trapped light over long distances that would have been otherwise impossible in conventional suspensions with positive polarizabilities. What greatly facilitates this behavior is an induced saturable nonlinear optical response introduced by the thermodynamic properties of these colloidal systems. This in turn leads to a substantial reduction in scattering via self-activated transparency effects. Our results may open up new opportunities in developing soft-matter systems with tunable optical nonlinearities.

cond-mat.soft↗
arXiv2013

Effect of Spin Accumulation at Co/Pt Interfaces on Anomalous Hall Effect in Pt/Co/Pt Trilayers

As current flows through a Pt/Co/Pt trilayer, spin Hall effect induced by charge current in the Pt layer leads to spin accumulation at the Co/Pt interfaces. Our experiment and calculation show an indication of the effect of spin accumulation at the Co/Pt interfaces on anomalous Hall coefficient in the Pt/Co/Pt sandwich, which depends on the Pt layer thickness and spin diffusion length in Pt layer. The ratio of the longitudinal current in the Pt cap layer due to anomalous Hall effect to the injected transverse current in the Co layer increases with the Pt cap layer thickness.

cond-mat.mtrl-sci↗
arXiv2013

Collective effects of multi-scatterer on coherent propagation of photon in a two dimensional network

We study the collective phenomenon in the scattering of a single-photon by one or two layers of two-level atoms. By modeling the photon dispersion with a two-dimensional (2D) coupled cavity array, we analytically derive the scattering probability of a single-photon. It is discovered that in the case with one layer of atoms, the atomic collective excitation leads to a shift for the single-photon scattering spectrum. Such a shift is related to the density of the atomic ensemble. For the case with two layers of atoms, an inter-layer effective coupling appears and induces an electromagnetic-induced-transparency-like phenomenon for the single-photon scattering. Our result provides a new scheme of analyzing photon coherent transport in 2D and may help to understand the current experiments about the high energy photon scattering by the layer nuclei material.

quant-ph↗
arXiv2013

The resilience of interdependent transportation networks under targeted attack

Modern world builds on the resilience of interdependent infrastructures characterized as complex networks. Recently, a framework for analysis of interdependent networks has been developed to explain the mechanism of resilience in interdependent networks. Here we extend this interdependent network model by considering flows in the networks and study the system's resilience under different attack strategies. In our model, nodes may fail due to either overload or loss of interdependency. Under the interaction between these two failure mechanisms, it is shown that interdependent scale-free networks show extreme vulnerability. The resilience of interdependent SF networks is found in our simulation much smaller than single SF network or interdependent SF networks without flows.

physics.soc-ph↗
arXiv2013

Scattering and effective interactions of ultracold atoms with spin-orbit coupling

We derive an analytical expression for the scattering amplitude of two ultracold atoms of arbitrary spin and with general spin-orbit (SO) coupling, on the basis of our recent work (Phys. Rev. A \textbf{86}, 053608 (2012)). As an application, we demonstrate that SO coupling can induce scattering resonance in the case with finite scattering length. The same approach can be applied to calculate the two-body bound state of SO-coupled ultracold atoms. For the ultracold spin-1/2 fermi gases in three- or two- dimensional systems with SO coupling, we also obtain the renormalization relation of effective contact interaction with momentum cutoff, as well as the applicability of Huang-Yang pseudo-potential.

cond-mat.quant-gas↗
arXiv2013

Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion

The superradiant Rayleigh scattering using a pump laser incident along the short axis of a Bose-Einstein condensate with a density distortion is studied, where the distortion is formed by shocking the condensate utilizing the residual magnetic force after the switching-off of the trapping potential. We find that very small variation of the atomic density distribution would induce remarkable asymmetrically populated scattering modes by the matter-wave superradiance with long time pulse. The optical field in the diluter region of the atomic cloud is more greatly amplified, which is not an ordinary mode amplification with the previous cognition. Our numerical simulations with the density envelop distortion are consistent with the experimental results. This supplies a useful method to reflect the geometric symmetries of the atomic density profile by the superradiance scattering.

cond-mat.quant-gas↗
arXiv2013

Spin-Orbit Coupling Induced Coherent Production of Feshbach Molecules in a Degenerate Fermi Gas

In this work we demonstrate a dynamic process in which SO coupling can coherently produce s-wave Feshbach molecules from a fully polarized Fermi gas, and can induce a coherent oscillation between Feshbach molecules and spin polarized gas. For comparison, we also show that such phenomena are absent if the inter-component coupling is momentum-independent. This demonstrates experimentally that SO coupling does provide finite matrix element between a singlet state and a triplet state, and therefore, implies the bound pairs of a system with SO coupling have triplet p-wave component, which can become topological superfluid by further cooling these pairs to condensation and confining them to lower dimension.

cond-mat.quant-gas↗
arXiv2013

Space-time crystals of trapped ions

Spontaneous symmetry breaking can lead to the formation of time crystals, as well as spatial crystals. Here we propose a space-time crystal of trapped ions and a method to realize it experimentally by confining ions in a ring-shaped trapping potential with a static magnetic field. The ions spontaneously form a spatial ring crystal due to Coulomb repulsion. This ion crystal can rotate persistently at the lowest quantum energy state in magnetic fields with fractional fluxes. The persistent rotation of trapped ions produces the temporal order, leading to the formation of a space-time crystal. We show that these space-time crystals are robust for direct experimental observation. We also study the effects of finite temperatures on the persistent rotation. The proposed space-time crystals of trapped ions provide a new dimension for exploring many-body physics and emerging properties of matter.

quant-ph↗
arXiv2013

Effective preparation and collisional decay of atomic condensate in excited bands of an optical lattice

We present a method for the effective preparation of a Bose-Einstein condensate (BEC) into the excited bands of an optical lattice via a standing-wave pulse sequence. With our method, the BEC can be prepared in either a single Bloch state in a excited-band, or a coherent superposition of states in different bands. Our scheme is experimentally demonstrated by preparing a $^{87}$Rb BEC into the $d$-band and the superposition of $s$- and $d$-band states of a one-dimensional optical lattice, within a few tens of microseconds. We further measure the decay of the BEC in the $d$-band state, and carry an analytical calculation for the collisional decay of atoms in the excited-band states. Our theoretical and experimental results consist well.

cond-mat.quant-gas↗
arXiv2013

Steady-state traffic flow on a ring road with up- and down- slopes

This paper studies steady-state traffic flow on a ring road with up- and down- slopes using a semi-discrete model. By exploiting the relations between the semi-discrete and the continuum models, a steady-state solution is uniquely determined for a given total number of vehicles on the ring road. The solution is exact and always stable with respect to the first-order continuum model, whereas it is a good approximation with respect to the semi-discrete model provided that the involved equilibrium constant states are linearly stable. In an otherwise case, the instability of one or more equilibria could trigger stop-and-go waves propagating in certain road sections or throughout the ring road. The indicated results are reasonable and thus physically significant for a better understanding of real traffic flow on an inhomogeneous road.

math-ph↗