Current experimental realizations of the quantum anomalous Hall phase in both electronic and photonic systems have been limited to a Chern number of one. In photonics, this corresponds to a single-mode one-way edge waveguide. Here, we predict quantum anomalous Hall phases in photonic crystals with large Chern numbers of 2, 3, and 4. These new topological phases were found by simultaneously gapping multiple Dirac and quadratic points. We demonstrate a continuously tunable power splitter as a possible application of multimode one-way waveguides. All our findings are readily realizable at microwave frequencies.

We examine the statistical properties of nonlinear random waves that are ruled by the one-dimensional defocusing and integrable nonlinear Schrödinger equation. Using fast detection techniques in an optical fiber experiment, we observe that the probability density function of light fluctuations is characterized by tails that are lower than those predicted by a Gaussian distribution. Moreover, by applying a bandpass frequency optical filter, we reveal the phenomenon of intermittency; i.e., small scales are characterized by large heavy-tailed deviations from Gaussian statistics, while the large ones are almost Gaussian. These phenomena are very well described by numerical simulations of the one-dimensional nonlinear Schrödinger equation.

Light-matter interaction gives optical microscopes tremendous versatility compared with other imaging methods such as electron microscopes, scanning probe microscopes, or x-ray scattering where there are various limitations on sample preparation and where the methods are inapplicable to bioimaging with live cells. However, this comes at the expense of a limited resolution due to the diffraction limit. Here, we demonstrate a novel method utilizing elastic scattering from disordered nanoparticles to achieve subdiffraction limited imaging. The measured far-field speckle fields can be used to reconstruct the subwavelength details of the target by time reversal, which allows full-field dynamic super-resolution imaging. The fabrication of the scattering superlens is extremely simple and the method has no restrictions on the wavelength of light that is used.

In partially miscible two-layer systems within a gravity field, buoyancy-driven convective motions can appear when one phase dissolves with a finite solubility into the other one. We investigate the influence of chemical reactions on such convective dissolution by a linear stability analysis of a reaction-diffusion-convection model. We show theoretically that a chemical reaction can either enhance or decrease the onset time of the convection, depending on the type of density profile building up in time in the reactive solution. We classify the stabilizing and destabilizing scenarios in a parameter space spanned by the solutal Rayleigh numbers. As an example, we experimentally demonstrate the possibility to enhance the convective dissolution of gaseous ${\mathrm{CO}}_2$ in aqueous solutions by a classical acid-base reaction.

We report experimental measurements of heat transport in rotating Rayleigh-Bénard convection in a cylindrical convection cell with an aspect ratio of $\mathrm{\Gamma }=1/2$. The fluid is helium gas with a Prandtl number $\mathrm{Pr}=0.7$. The range of control parameters for Rayleigh numbers $4\times {10}^9<\text{Ra}<4\times {10}^{11}$ and for Ekman numbers $2\times {10}^{-7}<\text{Ek}<3\times {10}^{-5}$ (corresponding to Taylor numbers $4\times {10}^9<\mathrm{Ta}<1\times {10}^{14}$ and convective Rossby numbers $0.07<\text{Ro}<5$). We determine the transition from weakly rotating turbulent convection to rotation dominated geostrophic convection through experimental measurements of the heat transport Nu. The heat transport, best collapsed using a parameter ${\mathrm{RaEk}}^{\beta }$ with $1.65<\beta <1.8$, defines two boundaries in the phase diagram of ${\text{Ra}/\text{Ra}}_c$ versus Ek and elucidates properties of the geostrophic turbulence regime of rotating thermal convection. We find $\mathrm{Nu}\sim {(\text{Ra}/{\text{Ra}}_c)}^{\gamma }$ with $\gamma \approx 1$ from direct measurement and $1.2<\gamma <1.6$ inferred from scaling arguments.

We study the time evolution of Ginibre matrices whose elements undergo Brownian motion. The non-Hermitian character of the Ginibre ensemble binds the dynamics of eigenvalues to the evolution of eigenvectors in a nontrivial way, leading to a system of coupled nonlinear equations resembling those for turbulent systems. We formulate a mathematical framework allowing simultaneous description of the flow of eigenvalues and eigenvectors, and we unravel a hidden dynamics as a function of a new complex variable, which in the standard description is treated as a regulator only. We solve the evolution equations for large matrices and demonstrate that the nonanalytic behavior of the Green’s functions is associated with a shock wave stemming from a Burgers-like equation describing correlations of eigenvectors. We conjecture that the hidden dynamics that we observe for the Ginibre ensemble is a general feature of non-Hermitian random matrix models and is relevant to related physical applications.

We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons. We demonstrate that these features are observed for negligible nonlinearity (i.e., polariton-polariton interaction) and are, therefore, not sufficient to identify dark and half-dark solitons. A linear model based on the Maxwell equations is shown to reproduce the experimental observations.

The transmission of information can couple two entities of very different nature, one of them serving as a memory for the other. Here we study the situation in which information is stored in a wave field and serves as a memory that pilots the dynamics of a particle. Such a system can be implemented by a bouncing drop generating surface waves sustained by a parametric forcing. The motion of the resulting “walker” when confined in a harmonic potential well is generally disordered. Here we show that these trajectories correspond to chaotic regimes characterized by intermittent transitions between a discrete set of states. At any given time, the system is in one of these states characterized by a double quantization of size and angular momentum. A low dimensional intermittency determines their respective probabilities. They thus form an eigenstate basis of decomposition for what would be observed as a superposition of states if all measurements were intrusive.

The experimentally measured input-output characteristics of optically pumped semiconductor microcavities exhibits unexpected oscillations modifying the fundamentally linear slope in the excitation power regime below lasing. A systematic microscopic analysis reproduces these oscillations, identifying them as a genuine quantum-memory effect, i.e., a photon-density correlation accumulated during the excitation. With the use of projected quantum measurements, it is shown that the input-output oscillations can be controlled and enhanced by an order of magnitude when the quantum fluctuations of the pump are adjusted.

By utilizing the vector nature of light as well as the inherent anisotropy of artificial meta-atoms, we investigate parity time symmetry breaking in polarization space using a metasurface with anisotropic absorption, whose building blocks consist of two orthogonally orientated meta-atoms with the same resonant frequency but different loss coefficients. By varying their coupling strength, we directly observe a phase transition in the eigenpolarization states of the system, across which the long axis of the eigenpolarization ellipses experience a sudden rotation of 45°. Despite the lack of rotational symmetry of the metasurface, precisely at the phase transition, known as the exceptional point, the eigenmodes coalesce into a single circularly polarized state. The $PT$ symmetric metasurfaces are experimentally implemented at terahertz frequencies.

We consider the inertial range spectrum of capillary wave turbulence. Under the assumptions of weak turbulence, the theoretical surface elevation spectrum scales with wave number $k$ as $I_{\eta }\sim k^{\alpha }$, where $\alpha ={\alpha }_0=-19/4$, energy (density) flux $P$ as $P^{1/2}$. The proportional factor $C$, known as the Kolmogorov constant, has a theoretical value of $C=C_0=9.85$ (we show that this value holds only after a formulation in the original derivation is corrected). The $k^{-19/4}$ scaling has been extensively, but not conclusively, tested; the $P^{1/2}$ scaling has been investigated experimentally, but until recently remains controversial, while direct confirmation of the value of $C_0$ remains elusive. We conduct a direct numerical investigation implementing the primitive Euler equations. For sufficiently high nonlinearity, the theoretical $k^{-19/4}$ and $P^{1/2}$ scalings as well as value of $C_0$ are well recovered by our numerical results. For a given number of numerical modes $N$, as nonlinearity decreases, the long-time spectra deviate from theoretical predictions with respect to scaling with $P$, with calculated values of $\alpha <{\alpha }_0$ and $C>C_0$, all due to finite box effect.

A robust energy transfer mechanism is found in nonlinear wave systems, which favors transfers toward modes interacting via triads with nonzero frequency mismatch, applicable in meteorology, nonlinear optics and plasma wave turbulence. We emphasize the concepts of truly dynamical degrees of freedom and triad precession. Transfer efficiency is maximal when the triads’ precession frequencies resonate with the system’s nonlinear frequencies, leading to a collective state of synchronized triads with strong turbulent cascades at intermediate nonlinearity. Numerical simulations confirm analytical predictions.

The Bénard–von Kármán vortex shedding instability in the wake of a cylinder is perhaps the best known example of a supercritical Hopf bifurcation in fluid dynamics. However, a simplified physical description that accurately accounts for the saturation amplitude of the instability is still missing. Here, we present a simple self-consistent model that provides a clear description of the saturation mechanism and quantitatively predicts the saturated amplitude and flow fields. The model is formally constructed by a set of coupled equations governing the mean flow together with its most unstable eigenmode with finite size. The saturation amplitude is determined by requiring the mean flow to be neutrally stable. Without requiring any input from numerical or experimental data, the resolution of the model provides a good prediction of the amplitude and frequency of the vortex shedding as well as the spatial structure of the mean flow and the Reynolds stress.

We investigate theoretically high-harmonic generation (HHG) in bulk crystals exposed to intense midinfrared lasers with photon energies smaller than the band gap. The two main mechanisms, interband and intraband HHG, are explored. Our analysis indicates that the interband current neglected so far is the dominant mechanism for HHG. Saddle point analysis in the Keldysh limit yields an intuitive picture of interband HHG in solids similar to atomic HHG. Interband and intraband HHG exhibit a fundamentally different wavelength dependence. This signature can be used to experimentally distinguish between the two mechanisms in order to verify their importance.

A multiscale analysis of the spatially averaged velocity of an imbibition front $V_{\ell }(t)$ measured at scale $\ell$ reveals that the slow front dynamics is intermittent: the distributions of $\mathrm{\Delta }{V}_{\ell }(\tau )=V_{\ell }(t+\tau )-V_{\ell }(t)$ evolve continuously through time scales $\tau$, from heavy-tailed to Gaussian—reached at a time lag ${\tau }_c$ set by the extent of the medium heterogeneities. Intermittency results from capillary bursts triggered from the smallest scale of the disorder up to the scale ${\ell }_c$ at which viscous dissipation becomes dominant. The effective number of degrees of freedom of the front $\ell /{\ell }_c$ controls its intensity.

A drop of water deposited on a cold plate freezes into an ice drop with a pointy tip. While this phenomenon clearly finds its origin in the expansion of water upon freezing, a quantitative description of the tip singularity has remained elusive. Here we demonstrate how the geometry of the freezing front, determined by heat transfer considerations, is crucial for the tip formation. We perform systematic measurements of the angles of the conical tip, and reveal the dynamics of the solidification front in a Hele-Shaw geometry. It is found that the cone angle is independent of substrate temperature and wetting angle, suggesting a universal, self-similar mechanism that does not depend on the rate of solidification. We propose a model for the freezing front and derive resulting tip angles analytically, in good agreement with the experiments.