We present solid evidence for the existence of a well-defined Higgs amplitude mode in two-dimensional relativistic field theories based on analytically continued results from quantum Monte Carlo simulations of the Bose-Hubbard model in the vicinity of the superfluid–Mott insulator quantum critical point, featuring emergent particle-hole symmetry and Lorentz invariance. The Higgs boson, seen as a well-defined low-frequency resonance in the spectral density, is quickly pushed to high energies in the superfluid phase and disappears by merging with the broad secondary peak at the characteristic interaction scale. Simulations of a trapped system of ultracold ${}^{87}\mathrm{Rb}$ atoms demonstrate that the low-frequency resonance is lost for typical experimental parameters, while the characteristic frequency for the onset of a strong response is preserved.

In this Letter, we consider the variation of the entanglement entropy of a region as the shape of the entangling surface is changed. We show that the variation satisfies a Wess-Zumino-like integrability condition in field theories which can be consistently coupled to gravity. In this case, the “anomaly” is localized on the entangling surface. The solution of the integrability condition should give all the nontrivial finite local terms which can appear in the variation of the entanglement entropy. The answers depend on the intrinsic and extrinsic geometry of the entangling surface, but the form does not depend on the details of the field theory. The coefficients, which multiply the purely geometric contributions, will depend on the particular details of the field theory.

Though topological aspects of energy bands are known to play a key role in quantum transport in solid-state systems, the implications of Floquet band topology for transport in momentum space (i.e., acceleration) have not been explored so far. Using a ratchet accelerator model inspired by existing cold-atom experiments, here we characterize a class of extended Floquet bands of one-dimensional driven quantum systems by Chern numbers, reveal topological phase transitions therein, and theoretically predict the quantization of adiabatic transport in momentum space. Numerical results confirm our theory and indicate the feasibility of experimental studies.

Midinfrared strong-field laser ionization offers the promise of measuring holograms of atoms and molecules, which contain both spatial and temporal information of the ion and the photoelectron with subfemtosecond temporal and angstrom spatial resolution. We report on the scaling of photoelectron holographic interference patterns with the laser pulse duration, wavelength, and intensity. High-resolution holograms for the ionization of metastable xenon atoms by $7–16\mu \mathrm{m}$ light from the FELICE free electron laser are presented and compared to semiclassical calculations that provide analytical insight.

We experimentally and theoretically study the coincidence count rate for down-converted x-ray photons. Because of photoionization, parametric down-conversion at x-ray wavelengths generally involves loss and the theoretical description requires a Langevin approach. By working in a transmission geometry (Laue) rather than in the Bragg geometry of previous experiments, we obtain an improvement in the signal-to-noise ratio of 12.5, and find agreement between experiment and theory.

We describe how strong resonant interactions in multimode optomechanical systems can be used to induce controlled nonlinear couplings between single photons and phonons. Combined with linear mapping schemes between photons and phonons, these techniques provide a universal building block for various classical and quantum information processing applications. Our approach is especially suited for nano-optomechanical devices, where strong optomechanical interactions on a single photon level are within experimental reach.

We report on high-resolution, three-dimensional, high Rayleigh number, and low density ratio numerical simulations of fingering convection. We observe a previously unreported phenomenon of self-organization of fingers that cluster together to form larger-scale coherent structures. The flow ultimately forms density staircases, alternating well-mixed regions with fingering convective zones. We give evidence that the mechanical mixing induced by the clusters forms the staircases with a mechanism analogous to staircase formation in a stably stratified, nonconvective, stirred fluid.

This Letter describes the first experimental demonstration of the guiding of a relativistic electron beam in a solid target using two colinear, relativistically intense, picosecond laser pulses. The first pulse creates a magnetic field that guides the higher-current, fast-electron beam generated by the second pulse. The effects of intensity ratio, delay, total energy, and intrinsic prepulse are examined. Thermal and $K\alpha$ imaging show reduced emission size, increased peak emission, and increased total emission at delays of 4–6 ps, an intensity ratio of $10:1$ (second:first) and a total energy of 186 J. In comparison to a single, high-contrast shot, the inferred fast-electron divergence is reduced by 2.7 times, while the fast-electron current density is increased by a factor of 1.8. The enhancements are reproduced with modeling and are shown to be due to the self-generation of magnetic fields. Such a scheme could be of considerable benefit to fast-ignition inertial fusion.

Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.

We present a low-energy electron microscopy study of nucleation and growth of BDA on Cu(001) at low supersaturation. At sufficiently high coverage, a dilute BDA phase coexists with $c(8\times 8)$ crystallites. The real-time microscopic information allows a direct visualization of near-critical nuclei, determination of the supersaturation and the line tension of the crystallites, and, thus, derivation of the Gibbs free energy for nucleation. The resulting critical nucleus size nicely agrees with the measured value. Nuclei up to 4–6 times larger still decay with finite probability, urging reconsideration of the classic perception of a critical nucleus.

We show results of broadband dielectric measurements on the charge ordered, proposed to be multiferroic material ${\mathrm{LuFe}}_2{\mathrm{O}}_4$. The temperature and frequency dependence of the complex permittivity as investigated for temperatures above and below the charge-order transition near $T_{\mathrm{CO}}\approx 320\mathrm{K}$ and for frequencies up to 1 GHz can be well described by a standard equivalent-circuit model considering Maxwell-Wagner-type contacts and hopping induced ac conductivity. No pronounced contribution of intrinsic dipolar polarization could be found, and thus the ferroelectric character of the charge order in ${\mathrm{LuFe}}_2{\mathrm{O}}_4$ has to be questioned.

An unusual increase in the Seebeck coefficient with increasing charge carrier density is observed in pentacene thin film transistors. This behavior is interpreted as being due to a transition from hopping transport in static localized states to bandlike transport, occurring at temperatures below $\sim 250\mathrm{K}$. Such a transition can be expected for organic materials in which both static energetic disorder and dynamic positional disorder are important. While clearly visible in the temperature and density dependent Seebeck coefficient, the transition hardly shows up in the charge carrier mobility.

The evolution with thickness of the properties of quench-deposited homogeneous amorphous bismuth ($a$-Bi) thin films with a 14.67 Å amorphous antimony ($a$-Sb) underlayer has been studied. In contrast with the results of previous investigations on similar systems the transition between the insulating and superconducting regimes is not direct, but involves an intervening metallic regime over a range of thicknesses. For these metallic films the temperature dependencies of the resistances at temperatures above the metallic regime can be described by the Halperin-Nelson form suggesting the occurrence of a Berezinskii-Kosterlitz-Thouless (BKT) transition at lower temperatures. However, this transition never occurs as curves of $R(T)$ flatten out as temperature is reduced. We suggest that this phenomenon is evidence of a crossover between a classical regime of thermal vortex unbinding at high temperatures and a regime of macroscopic quantum tunneling at low temperatures. The latter prevents the BKT transition from occurring.

We experimentally demonstrate cascaded field enhancement by means of gold nanoparticle dimer and trimer antennas. The local field enhancement is probed by single-molecule fluorescence using fluorophores with high intrinsic quantum efficiency ($Q^0>80\%$). Using a self-similar trimer antenna consisting of 80, 40, and 20 nm gold nanoparticles, we demonstrate a fluorescence enhancement of 40 and a spatial confinement of 15 nm. Compared with a single gold nanoparticle, the self-similar trimer antenna improves the enhancement-confinement ratio by more than an order of magnitude. Self-similar antennas hold promise for high-resolution imaging and spectroscopy, ultrasensitive detection, and efficient single-photon sources.

Geometric frustration gives rise to new fundamental phenomena and is known to yield the formation of exotic states of matter, such as incommensurate crystals, modulated liquid-crystalline phases, and phases stabilized by defects. In this Letter, we present a detailed study of polar structure of freely suspended fluid filaments in a polarization modulated liquid-crystal phase. We show that a periodic pattern of polarization-splay stripes separated by defect boundaries and decorating smectic layers can stabilize the structure of fluid fibers against the Rayleigh-Plateau instability. The instability is suppressed by the resistance of the defect structure to a radial compression of the cylindrical fibers. Our results provide direct experimental observation of a link between the stability of the liquid fibers, internal polar order, and geometrical constraints. They open a new perspective on a wide range of fluid polar fiber materials.

Collective computation is typically polynomial in the number of computational elements, such as transistors or neurons, whether one considers the storage capacity of a memory device or the number of floating-point operations per second of a CPU. However, we show here that the capacity of a computational network to resolve real-valued signals of arbitrary dimensions can be exponential in $N$, even if the individual elements are noisy and unreliable. Nested, modular codes that achieve such high resolutions mirror the properties of grid cells in vertebrates, which underlie spatial navigation.

Cosmic superstrings interact generically with a tower of light and/or strongly coupled Kaluza-Klein (KK) modes associated with the geometry of the internal space. We study the production of KK particles by cosmic superstring loops, and show that it is constrained by big bang nucleosynthesis. We study the resulting constraints in the parameter space of the underlying string theory model and highlight their complementarity with the regions that can be probed by current and upcoming gravitational wave experiments.

A QCD analysis is reported of ATLAS data on inclusive $W^{\pm }$ and $Z$ boson production in $pp$ collisions at the LHC, jointly with $ep$ deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken $x\sim 0.01$. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low $x$. The ratio of the strange-to-down sea quark distributions is determined to be ${1.00}_{-0.28}^{+0.25}$ at absolute four-momentum transfer squared $Q^2=1.9{\mathrm{GeV}}^2$ and $x=0.023$.

We examine, both experimentally and theoretically, an interaction of tightly focused polarized light with a slit on a metal surface supporting plasmon-polariton modes. Remarkably, this simple system can be highly sensitive to the polarization of the incident light and offers a perfect quantum weak measurement tool with a built-in postselection in the plasmon-polariton mode. We observe the plasmonic spin Hall effect in both coordinate and momentum spaces which is interpreted as weak measurements of the helicity of light with real and imaginary weak values determined by the input polarization. Our experiment combines the advantages of (i) quantum weak measurements, (ii) near-field plasmonic systems, and (iii) high-numerical aperture microscopy in employing the spin-orbit interaction of light and probing light chirality.

By combining scanning tunneling microscopy and spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory band calculations, we directly observe and resolve the one-dimensional edge states of single bilayer (BL) Bi(111) islands on clean ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ and Bi(111)-covered ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ substrates. The edge states are localized in the vicinity of step edges having an $\sim 2\mathrm{nm}$ wide spatial distribution in real space and reside in the energy gap of the Bi(111) BL. Our results demonstrate the existence of nontrivial topological edge states of single Bi(111) bilayer as a two-dimensional topological insulator.