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Angular oscillations can provide a useful probe of the superfluid properties of a system. Such measurements have recently been applied to dipolar supersolids, which exhibit both density modulation and phase coherence, and for which robust probes of superfluidity are particularly interesting. So far, these investigations have been confined to linear droplet arrays. Here, we explore angular oscillations in systems with 2D structure, which in principle have greater sensitivity to superfluidity. Surprisingly, in both experiment and simulation, we find that the frequency of angular oscillations remains nearly unchanged even when the superfluidity of the system is altered dramatically. This indicates that angular oscillation measurements do not always provide a robust experimental probe of superfluidity with typical experimental protocols., 4 pages, 4 figures more...

Energy transport in one-dimensional chains of particles with three conservation laws is generically anomalous and belongs to the Kardar-Parisi-Zhang dynamical universality class. Surprisingly, some examples where an apparent normal heat diffusion is found over a large range of length scales were reported. We propose a novel physical explanation of these intriguing observations. We develop a scaling analysis which explains how this may happen in the vicinity of an integrable limit, such as, but not only, the famous Toda model. In this limit, heat transport is mostly supplied by quasi-particles with a very large mean free path $\ell$. Upon increasing the system size $L$, three different regimes can be observed: a ballistic one, an intermediate diffusive range, and, eventually, the crossover to the anomalous (hydrodynamic) regime. Our theoretical considerations are supported by numerical simulations of a gas of diatomic hard-point particles for almost equal masses and of a weakly perturbed Toda chain. Finally, we discuss the case of the perturbed harmonic chain, which exhibits a yet different scenario., Comment: Published version more...

A new method (`explosive immunization' (EI)) is proposed for immunization and targeted destruction of networks. It combines the explosive percolation (EP) paradigm with the idea of maintaining a fragmented distribution of clusters. The ability of each node to block the spread of an infection (or to prevent the existence of a large cluster of connected nodes) is estimated by a score. The algorithm proceeds by first identifying low score nodes that should not be vaccinated/destroyed, analogously to the links selected in EP if they do not lead to large clusters. As in EP, this is done by selecting the worst node (weakest blocker) from a finite set of randomly chosen `candidates'. Tests on several real-world and model networks suggest that the method is more efficient and faster than any existing immunization strategy. Due to the latter property it can deal with very large networks., 9 pages, 9 figures. Supplemental material included as appendices more...

A powerful approach is proposed for the characterization of chaotic signals. It is based on the combined use of two classes of indicators: (i) the probability of suitable symbolic sequences (obtained from the ordinal patterns of the corresponding time series); (ii) the width of the corresponding cylinder sets. This way, much information can be extracted and used to quantify the complexity of a given signal. As an example of the potentiality of the method, I introduce a modified permutation entropy which allows for quantitative estimates of the Kolmogorov-Sinai entropy in hyperchaotic models, where other methods would be unpractical. As a by-product, estimates of the fractal dimension of the underlying attractors are possible as well. more...

We show that in generic one-dimensional Hamiltonian lattices the diffusion coefficient of the maximum Lyapunov exponent diverges in the thermodynamic limit. We trace this back to the long-range correlations associated with the evolution of the hydrodynamic modes. In the case of normal heat transport, the divergence is even stronger, leading to the breakdown of the usual single-function Family-Vicsek scaling ansatz. A similar scenario is expected to arise in the evolution of rough interfaces in the presence of suitably correlated background noise., D. P. acknowledges support by MINECO (Spain) under a Ramón y Cajal fellowship. We acknowledge support by MINECO (Spain) under Project No. FIS2014-59462-P. more...

We conjecture that in one-dimensional spatially extended systems the propagation velocity of correlations coincides with a zero of the convective Lyapunov spectrum. This conjecture is successfully tested in three different contexts: (i) a Hamiltonian system (a Fermi-Pasta-Ulam chain of oscillators); (ii) a general model for spatiotemporal chaos (the complex Ginzburg-Landau equation); (iii) experimental data taken from a CO2 laser with delayed feedback. In the last case, the convective Lyapunov exponent is determined directly from the experimental data. more...

We have imaged the stripe domain structure of perpendicularly magnetized fcc ultrathin Fe films grown on Cu(100). The stripe phase has a strong local orientational order and sustains the two kinds of fluctuations predicted by Abanov et al. [Phys. Rev. B 51, 1023 (1995)]: meandering and dislocations. Before reaching the Curie temperature, the stripes transform into a new and so far unobserved domain structure, characterized by domains with predominantly square corners. We argue that this phase is the tetragonal liquid phase proposed by Abanov et al. to separate the stripe phase from the paramagnetic phase. This two-step disordering is reminiscent of a two-dimensional melting process. more...

We discuss the thermal conductivity of a chain of coupled rotators, showing that it is the first example of a 1d nonlinear lattice exhibiting normal transport properties in the absence of an on-site potential. Numerical estimates obtained by simulating a chain in contact with two thermal baths at different temperatures are found to be consistent with those ones based on linear response theory. The dynamics of the Fourier modes provides direct evidence of energy diffusion. The finiteness of the conductivity is traced back to the occurrence of phase-jumps. Our conclusions are confirmed by the analysis of two variants of this model., 4 pages, 3 postscript figures more...

A nonlinear evolution equation for a vicinal surface growing in the step flow mode is derived in the limit of weak desorption. This limit turns out to be singular, and nonlinearities of arbitrary order need to be taken into account. The meandering instability caused by step edge barriers leads to a step morphology with a fixed meander wavelength, cusp singularities, and a step width increasing as $\sqrt{t}$ without bound. Full lattice gas simulations confirm this picture, and the observed step morphology is derived analytically from the evolution equation. more...

A novel class of nonequilibrium phase-transitions at zero temperature is found in chains of nonlinear oscillators.For two paradigmatic systems, the Hamiltonian XY model and the discrete nonlinear Schr\"odinger equation, we find that the application of boundary forces induces two synchronized phases, separated by a non-trivial interfacial region where the kinetic temperature is finite. Dynamics in such supercritical state displays anomalous chaotic properties whereby some observables are non-extensive and transport is superdiffusive. At finite temperatures, the transition is smoothed, but the temperature profile is still non-monotonous., Comment: Published version, minor changes more...

A simple two dimensional model of a phase growing on a substrate is introduced. The model is characterized by an adsorption rate q, and a desorption rate p. It exhibits a wetting transition which may be viewed as an unbinding transition of an interface from a wall. For p=1, the model may be mapped onto an exactly soluble equilibrium model exhibiting complete wetting with critical exponents gamma = 1/3 for the diverging interface width and x_0 = 1 for the zero-level occupation. For 0 < p != 1 a crossover to different exponents is observed which is related to a KPZ type nonlinearity., revised version, 4 pages, RevTeX, including 2 eps figures more...

We numerically study heat conduction in chains of nonlinear oscillators with time-reversible thermostats. A nontrivial temperature profile is found to set in, which obeys a simple scaling relation for increasing the number $N$ of particles. The thermal conductivity diverges approximately as ${N}^{1/2}$, indicating that chaotic behavior is not enough to ensure the Fourier law. Finally, we show that the microscopic dynamics ensures fulfillment of a macroscopic balance equation for the entropy production. more...

The complexity exhibited by cellular automata is studied using both topological (graph-theoretical)and metric (thermodynamic) techniques. A novel topological classification, based on a hierarchy oflanguages, is introduced. In particular, it is shown that the elementary rule 22 is able to produce, uponiteration, a deep nesting of grammatical rules and that this asymptotically yields a phase transition whenthe thermodynamic formalism is applied to the limit spatial configuration. [S0031-9007(96)02188-6] more...

Operating reconfigurable quantum circuits with single photon sources is a key goal of photonic quantum information science and technology. We use an integrated waveguide device containing directional couplers and a reconfigurable thermal phase controller to manipulate single photons emitted from a chromium related color center in diamond. Observation of both a wavelike interference pattern and particlelike sub-Poissionian autocorrelation functions demonstrates coherent manipulation of single photons emitted from the chromium related center and verifies wave particle duality. © 2013 American Physical Society. more...

Crystal surfaces may undergo thermodynamical as well kinetic, out-of-equilibrium instabilities. We consider the case of mound and pyramid formation, a common phenomenon in crystal growth and a long-standing problem in the field of pattern formation and coarsening dynamics. We are finally able to attack the problem analytically and get rigorous results. Three dynamical scenarios are possible: perpetual coarsening, interrupted coarsening, and no coarsening. In the perpetual coarsening scenario, mound size increases in time as L=t^n, where the coasening exponent is n=1/3 when faceting occurs, otherwise n=1/4., Comment: Changes in the final part. Accepted for publication in Phys. Rev. Lett more...

In a laser with delayed feedback operating in an oscillatory regime, phase defects appear for delays longer than the oscillation period. These defects are visualized by rearranging the data in a two-dimensional representation. Two distinct disordered phases are observed, one of weak turbulence characterized by phase fluctuations, and one of highly developed turbulence characterized by a constant density of defects. The transition between the two regimes is analyzed by studying the dependence of the defect lifetime on the delay. The experimental findings are modeled via a generalized Landau equation which includes a delayed coupling. more...

We report a novel approach to the question of whether and how the ground state can be achieved in square artificial spin ices where frustration is incomplete. We identify two types of disorder: quenched disorder in the island response to fields and disorder in the sequence of driving fields. Numerical simulations show that quenched disorder can lead to final states with lower energy, and disorder in the driving fields always lowers the final energy attained by the system. We use a network picture to understand these two effects: disorder in island responses creates new dynamical pathways, and disorder in driving fields allows more pathways to be followed., Comment: 5 pages, 5 figures more...

In this Letter we show that the analysis of Lyapunov-exponents fluctuations contributes to deepen our understanding of high-dimensional chaos. This is achieved by introducing a Gaussian approximation for the large deviation function that quantifies the fluctuation probability. More precisely, a diffusion matrix $\bf D$ (a dynamical invariant itself) is measured and analysed in terms of its principal components. The application of this method to three (conservative, as well as dissipative) models, allows: (i) quantifying the strength of the effective interactions among the different degrees of freedom; (ii) unveiling microscopic constraints such as those associated to a symplectic structure; (iii) checking the hyperbolicity of the dynamics., 4 pages, 3 figures. To appear in Phys. Rev. Lett more...

Generating quantum entanglement is not only an important scientific endeavor, but will be essential to realizing quantum-enhanced technologies, in particular, quantum-enhanced measurements with precision beyond classical limits. We investigate the heralded generation of multiphoton entanglement for quantum metrology using a reconfigurable integrated waveguide device in which projective measurement of auxiliary photons heralds the generation of path-entangled states. We use four and six-photon inputs, to analyze the heralding process of two- and four-photon NOON states-a superposition of N photons in two paths, capable of enabling phase supersensitive measurements at the Heisenberg limit. Realistic devices will include imperfections; as part of the heralded state preparation, we demonstrate phase superresolution within our chip with a state that is more robust to photon loss. more...

Using a combination of analytical and numerical techniques, we show that chaos in globally-coupled identical dynamical systems, be they dissipative or Hamiltonian, is both extensive and sub-extensive: their spectrum of Lyapunov exponents is asymptotically flat (thus extensive) at the value $\lambda_0$ given by a single unit forced by the mean-field, but sandwiched between sub-extensive bands containing typically $\mathcal{O}(\log N)$ exponents whose values vary as $\lambda \simeq \lambda_\infty + c/\log N$ with $\lambda_\infty \neq \lambda_0$., Comment: 4 pages, 4 figures; minor changes made and 2 figure panels added more...

Quantum computing promises to exploit the laws of quantum mechanics for processing information in ways fundamentally different from today's classical computers, leading to unprecedented efficiency. One-way quantum computation, sometimes referred to as the cluster model of quantum computation, is a very promising approach to fulfil the capabilities of quantum information processing. The cluster model is realizable through measurements on a highly entangled cluster state with no need for controlled unitary evolutions. Here we demonstrate unconditional one-way quantum computation experiments for continuous variables using a linear cluster state of four entangled optical modes. We implement an important set of quantum operations, linear transformations, in the optical phase space through one-way computation. Though not sufficient, these are necessary for universal quantum computation over continuous variables, and in our scheme, in principle, any such linear transformation can be unconditionally and deterministically applied to arbitrary single-mode quantum states., Comment: 9 pages, 3 figures more...

The interlayer exchange coupling in Fe(110)/Ag(111) multilayer structures with parallel alignment of the Fe layer magnetizations has been investigated with a zero-field M\"ossbauer spectroscopy technique that is sensitive only to the spin-wave spectrum at the Fe/Ag interface. Model spin-wave calculations are presented to connect the coupling strength to the observed interfacial spin-wave behavior. As the Ag thickness was varied from 0 to 40 ML (monolayers), the interfacial spectra of the films showed oscillations in the coupling strength with a period of 6 ML, in close agreement with recent predictions. more...

We investigate a network of integrate-and-fire neurons characterized by a distribution of spiking frequencies. Upon increasing the coupling strength, the model exhibits a transition from an asynchronous regime to a nontrivial collective behavior. Numerical simulations of large systems indicate that, at variance with the Kuramoto model, (i) the macroscopic dynamics stays irregular and (ii) the microscopic (single-neuron) evolution is linearly stable. more...

Coupled H\'enon maps are introduced to model in a more appropriate way chaos in extended systems. An effective technique allows the extraction of spatiotemporal periodic orbits, which are then used to approximate the invariant measure. A further implementation of the \ensuremath{\zeta}-function formalism reveals the extensive character of entropies and dimensions, and allows the computation of the associated multifractal spectra. Finally, the analysis of short chains indicates the existence of distinct phases in the invariant measure, characterized by a different number of positive Lyapunov exponents. more...

Expérience au LNS; International audience; A new reaction mechanism of violent reseparation of a heavy nucleus-nucleus system, $^{197}$Au + $^{197}$Au, into three or four massive fragments in collisions at 15 MeV=nucleon has been observed. After reseparation, the fragments are almost exactly aligned, thus showing a very short time scale of the reseparation process, of about 70–80 fm=c. more...

40Ca+;{40,48}Ca,46Ti reactions at 25 MeV/nucleon have been studied using the 4pi CHIMERA detector. An isospin effect on the competition between fusionlike and binarylike reaction mechanisms has been observed. The probability of producing a heavy residue is lower in the case of N approximately Z colliding systems as compared to the case of reactions induced on the neutron rich 48Ca target. Predictions based on constrained molecular dynamics II calculations show that the competition between fusionlike and binary reactions in the selected centrality bins can constrain the parametrization of the symmetry energy and its density dependence in the nuclear equation of state. more...

A new reaction mechanism of violent reseparation of a heavy nucleus-nucleus system, {sup 197}Au+{sup 197}Au, into three or four massive fragments in collisions at 15 MeV/nucleon has been observed. After reseparation, the fragments are almost exactly aligned, thus showing a very short time scale of the reseparation process, of about 70-80 fm/c. more...

A Comment on the Letter by Trieu Mai, Abhishek Dhar, and Onuttom Narayan, Phys. Rev. Lett. 98, 184301 (2007). The authors of the Letter offer a Reply.

A general method to determine covariant Lyapunov vectors in both discrete- and continuous-time dynamical systems is introduced. This allows to address fundamental questions such as the degree of hyperbolicity, which can be quantified in terms of the transversality of these intrinsic vectors. For spatially extended systems, the covariant Lyapunov vectors have localization properties and spatial Fourier spectra qualitatively different from those composing the orthonormalized basis obtained in the standard procedure used to calculate the Lyapunov exponents., Comment: 4 pages, 3 figures, submitted to Physical Review letters more...

Dynamics of a one-dimensional growing front with an unstable straight profile are analyzed. We argue that a coarsening process occurs if and only if the period \lambda of the steady state solution is an increasing function of its amplitude A. This statement is rigorously proved for two important classes of conserved and nonconserved models by investigating the phase diffusion equation of the steady pattern. We further provide clear numerical evidences for the growth equation of a stepped crystal surface., Comment: 4 pages. Corrected one mistake in the phase diffusion coefficient, Eq.(11). Accepted for publication in Physical Review Letters more...

The interpretation of delayed dynamical systems (DDS) in terms of a suitable spatiotemporal dynamics is put on a rigorous ground by deriving amplitude equations in the vicinity of a Hopf bifurcation. We show that comoving Lyapunov exponents can be defined and computed in a DDS. From the propagation of localized infinitesimal disturbances in DDS, we show the existence of convective type instabilities. Moreover, a widely studied class of DDS is mapped onto an evolution rule for a spatial system with drift and diffusion. more...

We present a theoretical study of magnetic relaxation of big molecules, M${\mathrm{n}}_{12}$${\mathrm{O}}_{12}$, at low temperature, when the relaxation time $\ensuremath{\tau}$ is temperature independent. If the magnetic field ${h}_{z}$ is not too low, tunneling can only take place if energy is exchanged with phonons. Then, $1/\ensuremath{\tau}\ensuremath{\sim}{h}_{z}^{3}$ for weak ${h}_{z}$. A steeper increase is expected for higher ${h}_{z}$. The effect of a transverse field ${h}_{x}$ is small. The maximum of $\ensuremath{\tau}({h}_{z})$ observed experimentally at ${h}_{z}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2$ T might be due to tunneling without phonons in low field, with a relaxation rate reduced by hyperfine interactions. more...