Analyzing coexistence and survival scenarios of Lotka-Volterra (LV) networks in which the total biomass is conserved is of vital importance for the characterization of long-term dynamics of ecological communities. Here, we introduce a classification scheme for coexistence scenarios in these conservative LV models and quantify the extinction process by employing the Pfaffian of the network’s interaction matrix. We illustrate our findings on global stability properties for general systems of four and five species and find a generalized scaling law for the extinction time.

The most conspicuous trait of collective animal behavior is the emergence of highly ordered structures. Less obvious to the eye, but perhaps more profound a signature of self-organization, is the presence of long-range spatial correlations. Experimental data on starling flocks in 3D show that the exponent ruling the decay of the velocity correlation function, $C(r)\sim 1/r^{\gamma }$, is extremely small, $\gamma \ll 1$. This result can neither be explained by equilibrium field theory nor by off-equilibrium theories and simulations of active systems. Here, by means of numerical simulations and theoretical calculations, we show that a dynamical field applied to the boundary of a set of Heisenberg spins on a 3D lattice gives rise to a vanishing exponent $\gamma$, as in starling flocks. The effect of the dynamical field is to create an information inflow from border to bulk that triggers long-range spin-wave modes, thus giving rise to an anomalously long-ranged correlation. The biological origin of this phenomenon can be either exogenous—information produced by environmental perturbations is transferred from boundary to bulk of the flock—or endogenous—the flock keeps itself in a constant state of dynamical excitation that is beneficial to correlation and collective response.

Recent advances in fields ranging from cosmology to computer science have hinted at a possible deep connection between intelligence and entropy maximization, but no formal physical relationship between them has yet been established. Here, we explicitly propose a first step toward such a relationship in the form of a causal generalization of entropic forces that we find can cause two defining behaviors of the human “cognitive niche”—tool use and social cooperation—to spontaneously emerge in simple physical systems. Our results suggest a potentially general thermodynamic model of adaptive behavior as a nonequilibrium process in open systems.

We propose a new measure to characterize the dimension of complex networks based on the ergodic theory of dynamical systems. This measure is derived from the correlation sum of a trajectory generated by a random walker navigating the network, and extends the classical Grassberger-Procaccia algorithm to the context of complex networks. The method is validated with reliable results for both synthetic networks and real-world networks such as the world air-transportation network or urban networks, and provides a computationally fast way for estimating the dimensionality of networks which only relies on the local information provided by the walkers.

We propose an experimentally accessible, objective measure for the macroscopicity of superposition states in mechanical quantum systems. Based on the observable consequences of a minimal, macrorealist extension of quantum mechanics, it allows one to quantify the degree of macroscopicity achieved in different experiments.

We demonstrate the direct generation of polarization-entangled photon pairs at room temperature and telecom wavelength in an AlGaAs semiconductor waveguide. The source is based on spontaneous parametric down-conversion with a counterpropagating phase-matching scheme. The quality of the two-photon state is assessed by the reconstruction of the density matrix giving a raw fidelity to a Bell state of 0.83; a theoretical model, taking into account the experimental parameters, provides ways to understand and control the amount of entanglement. Its compatibility with electrical injection, together with the high versatility of the generated two-photon state, make this source an attractive candidate for completely integrated quantum photonics devices.

Scalar atomic magnetometers have many attractive features but their sensitivity has been relatively poor. We describe a Rb scalar gradiometer using two multipass optical cells. We use a pump-probe measurement scheme to suppress spin-exchange relaxation and two probe pulses to find the spin precession zero crossing times with a resolution of 1 psec. We realize a magnetic field sensitivity of $0.54\mathrm{fT}/{\mathrm{Hz}}^{1/2}$, which improves by an order of magnitude the best scalar magnetometer sensitivity and exceeds, for example, the quantum limit set by the spin-exchange collisions for a scalar magnetometer with the same measurement volume operating in a continuous regime.

Perturbative gluon exchange interaction between quark and antiquark, or in a $3q$ system, is enhanced in a magnetic field and may cause vanishing of the total $q\overline{q}$ or $3q$ mass, and even unlimited decrease of it—recently called the magnetic collapse of QCD. The analysis of the one-loop correction below shows a considerable softening of this phenomenon due to $q\overline{q}$ loop contribution, similar to the Coulomb case of QED, leading to approximately logarithmic damping of gluon exchange interaction ($⟨V⟩\approx \mathcal{O}(1/\ln |eB|)$) at large magnetic field.

We report the calculation of next-to-next-to-leading order QCD corrections in the purely gluonic channel to dijet production and related observables at hadron colliders. Our result represents the first next-to-next-to-leading order calculation of a massless jet observable at hadron colliders, and opens the path towards precision QCD phenomenology with the LHC.

We have observed single photon double $K$-shell photoionization in the ${\mathrm{C}}_2{\mathrm{H}}_{2n}$ ($n=1–3$) hydrocarbon sequence and in ${\mathrm{N}}_2$ and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the $K^{-2}$ process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule ($K^{-1}{K}^{-1}$ process). In the ${\mathrm{C}}_2{\mathrm{H}}_{2n}$ sequence, the spectroscopy of $K^{-1}{K}^{-1}$ states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single $K$-shell ionization. The cross section variation for single photon $K^{-1}{K}^{-1}$ double core ionization in the ${\mathrm{C}}_2{\mathrm{H}}_{2n}$ sequence and in the isoelectronic ${\mathrm{C}}_2{\mathrm{H}}_2$, ${\mathrm{N}}_2$ and CO molecules validates a knock-out mechanism in which a primary ionized $1s$ photoelectron ejects another $1s$ electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

We introduce and study the properties of an array of QED cavities coupled by nonlinear elements, in the presence of photon leakage and driven by a coherent source. The nonlinear couplings lead to photon hopping and to nearest-neighbor Kerr terms. By tuning the system parameters, the steady state of the array can exhibit a photon crystal associated with a periodic modulation of the photon blockade. In some cases, the crystalline ordering may coexist with phase synchronization. The class of cavity arrays we consider can be built with superconducting circuits of existing technology.

It is shown that a single-layer array of high electric permittivity (high-$\epsilon$) rods with a radius smaller than $\lambda /10$ is capable of reflecting more than 97% of the energy of optical waves with an arbitrary incident angle. Here, $\lambda$ is the incident wavelength. The occurrence of the phenomenon depends on the construction of two particular grating modes (GMs) in the array which result in two corresponding transmitted wave components that cancel each other. The construction of the dominant GMs in the array benefits from the highly independent manipulability of the angular momenta components with opposite signs in high-$\epsilon$ particles. The effect offers the possibility to improve the optical elements integration level in on-chip optical circuits.

Beam divergences of high-order extreme ultraviolet harmonics from intense laser interactions with steep plasma density gradients are studied through experiment and Fourier analysis of the harmonic spatial phase. We show that while emission due to the relativistically oscillating mirror mechanism can be explained by ponderomotive surface denting, in agreement with previous results, the divergence of the emission due to the coherent wake emission mechanism requires a combination of the dent phase and an intrinsic emission phase. The temporal dependence of the divergences for both mechanisms is highlighted while it is also shown that the coherent wake emission divergence can be small in circumstances where the phase terms compensate each other.

Recently, optical lattices with nonzero Berry’s phases of Bloch bands have been realized. New approaches for measuring Berry’s phases and topological properties of bands with experimental tools appropriate for ultracold atoms need to be developed. In this Letter, we propose an interferometric method for measuring Berry’s phases of two-dimensional Bloch bands. The key idea is to use a combination of Ramsey interference and Bloch oscillations to measure Zak phases, i.e., Berry’s phases for closed trajectories corresponding to reciprocal lattice vectors. We demonstrate that this technique can be used to measure the Berry curvature of Bloch bands, the $\pi$ Berry’s phase of Dirac points, and the first Chern number of topological bands. We discuss several experimentally feasible realizations of this technique, which make it robust against low-frequency magnetic noise.

Ionic species often play important roles in chemical reactions occurring in water and other solvents, but it has been elusive to determine the solvent-dependent molecular structure with atomic resolution. The triiodide ion has a molecular structure that sensitively changes depending on the type of solvent and its symmetry can be broken by strong solute-solvent interaction. Here, by applying pump-probe x-ray solution scattering, we characterize the exact molecular structure of $\mathrm{I}_3{}^{-}$ ion in water, methanol, and acetonitrile with subangstrom accuracy. The data reveal that $\mathrm{I}_3{}^{-}$ ion has an asymmetric and bent structure in water. In contrast, the ion keeps its symmetry in acetonitrile, while the symmetry breaking occurs to a lesser extent in methanol than in water. The symmetry breaking of $\mathrm{I}_3{}^{-}$ ion is reproduced by density functional theory calculations using 34 explicit water molecules, confirming that the origin of the symmetry breaking is the hydrogen-bonding interaction between the solute and solvent molecules.

The growth dynamics of a single crack in a heterogeneous material under subcritical loading is an intermittent process, and many features of this dynamics have been shown to agree with simple models of thermally activated rupture. In order to better understand the role of material heterogeneities in this process, we study the subcritical propagation of a crack in a sheet of paper in the presence of a distribution of small defects such as holes. The experimental data obtained for two different distributions of holes are discussed in the light of models that predict the slowing down of crack growth when the disorder in the material is increased; however, in contradiction with these theoretical predictions, the experiments result in longer lasting cracks in a more ordered scenario. We argue that this effect is specific to subcritical crack dynamics and that the weakest zones between holes at close distance to each other are responsible for both the acceleration of the crack dynamics and the slightly different roughness of the crack path.

Binary blends of polystyrene with oligostyrene are perfectly miscible ($\chi =0$) yet dynamically heterogeneous. This is evidenced by independent probing of the dipole relaxation perpendicular to the backbone by dielectric spectroscopy and molecular dynamics. The self-concentration model with a single intramolecular length scale qualitatively describes the slower segmental dynamics. A quantitative comparison based on MD, however, requires a composition-dependent length scale. The pertinent dynamic length scale that best describes the slow segmental dynamics in miscible blends relates to both intra- and intermolecular contributions.

In this Letter we present the detailed, quantitative comparison between experimentally and theoretically derived structures of the extended $\{311\}$ defect in silicon. Agreement between experimental and theoretical column positions of better than $\pm 0.05\mathrm{nm}$ has been achieved for all 100 atomic columns in the defect structure. This represents a calculated density of $5.5\times {10}^{14}$ silicon interstitials per ${\mathrm{cm}}^2$ on $\{311\}$ planes, in agreement with previous work [S. Takeda, Jpn. J. Appl. Phys., Part 2, 30, L639 (1991)]. We show that although the $\{311\}$ defect is made up of five-, six-, seven-, and eight-member rings, the shape of these rings varies as a function of position along the defect, and these variations can be determined experimentally with high precision and accuracy. The excellent agreement between the calculated and experimentally derived structure, including the position of atomic columns and the shape of the distinct structural units of the defect, provides strong evidence for the quality and robustness of the molecular dynamics simulation approach for structural studies of defects. The experimental approach is straightforward, without the need for complicated image processing methods, and is therefore widely applicable.

The elastic response of suspended ${\mathrm{NbSe}}_3$ nanowires is studied across the charge density wave phase transition. The nanoscale dimensions of the resonator lead to a large resonant frequency ($\sim 10–100\mathrm{MHz}$), bringing the excited phonon frequency in close proximity of the plasmon mode of the electronic condensate—a parameter window not accessible in bulk systems. The interaction between the phonon and plasmon modes strongly modifies the elastic properties at high frequencies. This is manifested in the nanomechanics of the system as a sharp peak in the temperature dependence of the elastic modulus (relative change of 12.8%) in the charge density wave phase.

Cyclotron spin-flip excitation in a $\nu =2$ quantum Hall system, being separated from the ground state by a slightly smaller gap than the cyclotron energy and from upper magnetoplasma excitation by the Coulomb gap [S. Dickmann and I. V. Kukushkin, Phys. Rev. B 71, 241310(R) (2005); L. V. Kulik, I. V. Kukushkin, S. Dickmann, V. E. Kirpichev, A. B. Van’kov, A. L. Parakhonsky, J. H. Smet, K. von Klitzing, and W. Wegscheider, Phys. Rev. B 72, 073304 (2005)] cannot relax in a purely electronic way except only with the emission of a shortwave acoustic phonon ($k\sim 3\times {10}^7/\mathrm{cm}$). As a result, relaxation in a modern wide-thickness quantum well occurs very slowly. We calculate the characteristic relaxation time to be $\sim 1\mathrm{s}$. Extremely slow relaxation should allow the production of a considerable density of zero-momenta cyclotron spin-flip excitations in a very small phase volume, thus forming a highly coherent ensemble—the Bose-Einstein condensate. The condensate state can be controlled by short optical pulses ($\lesssim 1\mu \mathrm{s}$), switching it on and off.