Interacting quantum walk on a graph

We introduce an elementary quantum system consisting of a set of spins on a graph and a particle hopping between its nodes. The quantum state is build sequentially, applying a unitary transformation that couples neighboring spins and, at a node, the local spin with the particle. We observe the relaxation of the system towards a stationary paramagnetic or ferromagnetic state, and demonstrate that it is related to eigenvectors thermalization and random matrix statistics. The relation between these macroscopic properties and interaction generated entanglement is discussed.Comment: 15 pages, 11 figures (v2 extended version

Edge states in a two-dimensional quantum walk with disorder

We investigate the effect of spatial disorder on the edge states localized at the interface between two topologically different regions. Rotation disorder can localize the quantum walk if it is strong enough to change the topology, otherwise the edge state is protected. Nonlinear spatial disorder, dependent on the walker's state, attracts the walk to the interface even for very large coupling, preserving the ballistic transport characteristic of the clean regime.Comment: extended new version; 10 pages, 10 figure

Vortex sheet dynamics and turbulence

The nonlinear evolution of a vortex sheet driven by the Kelvin--Helmholtz instability is characterized by the formation of a spiral possessing complex stretching and intensity patterns. We show that the power energy spectrum of a single two-dimensional vortex sheet tends to the usual fluid turbulent spectrum, with an exponent of -3. Using numerical simulations and asymptotic methods, we demonstrate the relation between this power law and the singularities in the geometry and vorticity distribution of the sheet.Comment: Submitted to Phys. Rev. Letters, the Dynamique des vortex Collaboratio

Is ECB Communication Effective?

In its Monthly Bulletin of November 2002, the European Central Bank (ECB) stated that the monthly press conference held by its President represents one of its most important communication channels and that it provides a comprehensive summary of the policy relevant assessment of economic developments. After providing a glossary to translate the qualitative information of the press conferences into an ordered scale, we verify empirically whether and to what extent market expectations react to the information released by the ECB. We found that the public not only understand but also believe the signals sent by the European monetary authority.communication, credibility, ECB, glossary, Repo, Euribor, news approach

Stock-bond correlation and the bond quality ratio: Removing the discount factor to generate a “deflated” stock index

This paper investigates the cyclical co-movements between US stocks and interest rates by testing a simple model where divergence between stock and bond price behavior is explained by “stock market strength,” where the latter depends on the market climate about future corporate profits—as captured by the corporate bond quality ratio—and an unexplained stock market sentiment. Using two different regression techniques to check for robustness, we find evidence of a statistically significant cyclical correlation between stocks and bonds. On the basis of this finding, we then present a methodology to “deflate” a stock price index such that we can compare stock market strength over time. This is obtained by removing the effect of a changing discount rate—as measured by our regressions—on stock prices. For example, viewed in this light, the past five years in the US stock market reveal a wider fluctuation in stock market strength than we can observe on the basis of stock price indices alone.Stock-bond correlation, Market sentiment, Stock price.

Topological changes of two-dimensional magnetic textures

We investigate the interaction of magnetic vortices and skyrmions with a spin-polarized current. In a square lattice, fixed classical spins and quantum itinerant electrons, evolve according to the coupled Landau-Lifshitz and Schr\"odinger equations. Changes in the topology occur at microscopic time and length scales, and are shown to be triggered by the nucleation of a nontrivial electron-spin structure at the vortex core.Comment: See supplementary material (high resolution figures and movies) https://drive.google.com/folderview?id=0By4j_RJ9SKLpQ2R5UklXLURvbEE&usp=sharing --- v2: Extended versio

The Importance of the Wording of the ECB

This paper analyses the ECB communication, focusing in particular on its transparency dimension. We posit that if the ECB is transparent about its future policy decisions, then we should be able to forecast fairly well its future interest rate setting behaviour. We find that the predicting ability of the European monetary authority's words, is similar to the one implied by market-based measures of monetary policy expectations. Moreover, the ECB's wording provides complementary, rather than substitute, information with respect to economic and monetary variables.ECB communication, transparency, monetary policy forecast, empirical reaction function, Euribor rate curve

Skyrmion collapse

We investigate the topological change of a Belavin-Polyakov skyrmion under the action of a spin-polarized current. The dynamics is described by the Schr\"odinger equation for the electrons carrying the current coupled to the Landau-Lifshitz equation for the evolution of the magnetic texture in a square lattice. We show that the addition of an exchange dissipation term, tends to smooth the transition from the skyrmion state to the ferromagnetic state. We demonstrate that this topological change, in the continuum dissipationless limit, can be described as a self-similar finite-time singularity by which the skyrmion core collapses.Comment: 9 pages, 6 figures; v2. discussion added (the title of the published version is "Skyrmion to ferromagnetic state transition: A description of the topological change as a finite-time singularity in the skyrmion dynamics"

Nonlinear evolution of a morphological instability in a strained epitaxial film

A strained epitaxial film deposited on a deformable substrate undergoes a morphological instability relaxing the elastic energy by surface diffusion. The nonlinear and nonlocal dynamical equations of such films with wetting interactions are derived and solved numerically in two and three dimensions. Above some critical thickness, the surface evolves towards an array of islands separated by a wetting layer. The island chemical potential decreases with its volume, so that the system experiences a non-interrupted coarsening described by power laws with a marked dimension dependence.Comment: 4 pages, 6 figure