We derive the ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ Green-Schwarz superstring from four-dimensional Beltrami-Chern-Simons theory reduced on a manifold with singular boundary conditions. In this construction, the Lax connection and spectral parameter of the integrable superstring have a simple geometric origin in four dimensions as gauge connection and reduction coordinate. $\kappa$ symmetry arises as a certain class of singular gauge transformations, while the world-sheet metric comes from complex-structure-changing Beltrami differentials. Our approach offers the possibility of investigating integrable holography using traditional field theory methods.

Reliable neutron-induced-reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative capture cross sections of ${}^{239}\mathrm{Pu}$ in a consistent manner from a single measurement. This was achieved by combining simultaneously measured fission and $\gamma$-emission probabilities for the ${}^{240}\mathrm{Pu}({}^4\mathrm{He},{}^4{\mathrm{He}}^{\prime })$ surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected $\gamma$-ray transitions, we measure the $\gamma$-emission probability. This enlarges the applicability of the surrogate-reaction method.

We experimentally and theoretically study phase coherence in two-component Bose-Einstein condensates of ${}^{87}\mathrm{Rb}$ atoms on an atom chip. Using Ramsey interferometry we determine the temporal decay of coherence between the $|F=1,m_F=-1⟩$ and $|F=2,m_F=+1⟩$ hyperfine ground states. We observe that the coherence is limited by random collisional phase shifts due to the stochastic nature of atom loss. The mechanism is confirmed quantitatively by a quantum trajectory method based on a master equation which takes into account collisional interactions, atom number fluctuations, and losses in the system. This decoherence process can be slowed down by reducing the density of the condensate. Our findings are relevant for experiments on quantum metrology and many-particle entanglement with Bose-Einstein condensates and the development of chip-based atomic clocks.

One of the central principles of quantum mechanics is that if there are multiple paths that lead to the same event and there is no way to distinguish between them, interference occurs. It is often assumed that distinguishing information in the preparation, evolution, or measurement of a system is sufficient to destroy interference. However, it is still possible for photons in distinguishable, separable states to interfere due to the indistinguishability of paths corresponding to possible exchange processes. Here we experimentally measure an interference signal that depends only on the multiparticle interference of four photons in a four-port interferometer despite pairs of them occupying distinguishable states.

Structured-Gaussian beams are shown to be fully and uniquely represented by a collection of points (or a constellation) on the surface of the modal Majorana sphere, providing a complete generalization of the modal Poincaré sphere to higher-order modes. The symmetries of this Majorana constellation translate into invariances to astigmatic transformations, giving way to continuous or quantized geometric phases. The experimental amenability of this system is shown by verifying the existence of both these symmetries and geometric phases.

The advent of high-speed x-ray photon correlation spectroscopy now allows the study of critical phenomena in fluids to much smaller length scales and over a wider range of temperatures than is possible with dynamic light scattering. We present an x-ray photon correlation spectroscopy study of critical fluctuation dynamics in a complex fluid typical of those used in liquid-liquid extraction (LLE) of ions, dodecane-DMDBTDMA with extracted aqueous $\mathrm{Ce}({\mathrm{NO}}_3{)}_3$. We observe good agreement with both static and dynamic scaling without the need for significant noncritical background corrections. Critical exponents agree with 3D Ising values, and the fluctuation dynamics are described by simple exponential relaxation. The form of the dynamic master curve deviates somewhat from the Kawasaki result, with a more abrupt transition between the critical and noncritical asymptotic behavior. The concepts of critical phenomena thus provide a quantitative framework for understanding the structure and dynamics of LLE systems and a path forward to new LLE processes.

More than thirty years ago, it was theoretically predicted that friction for incommensurate contacts between atomically smooth, infinite, crystalline materials (e.g., graphite, ${\mathrm{MoS}}_2$) is vanishing in the low speed limit, and this corresponding state was called structural superlubricity (SSL). However, experimental validation of this prediction has met challenges, since real contacts always have a finite size, and the overall friction arises not only from the atoms located within the contact area, but also from those at the contact edges which can contribute a finite amount of friction even when the incommensurate area does not. Here, we report, using a novel method, the decoupling of these contributions for the first time. The results obtained from nanoscale to microscale incommensurate contacts of graphite under ambient conditions verify that the average frictional contribution of an inner atom is no more than ${10}^{-4}$ that of an atom at the edge. Correspondingly, the total friction force is dominated by friction between the contact edges for contacts up to $10\mu \mathrm{m}$ in lateral size. We discuss the physical mechanisms of friction observed in SSL contacts, and provide guidelines for the rational design of large-scale SSL contacts.

Doping a topological insulator (TI) film with transition metal ions can break its time-reversal symmetry and lead to the realization of the quantum anomalous Hall (QAH) effect. Prior studies have shown that the longitudinal resistance of the QAH samples usually does not vanish when the Hall resistance shows a good quantization. This has been interpreted as a result of the presence of possible dissipative conducting channels in magnetic TI samples. By studying the temperature- and magnetic-field-dependence of the magnetoresistance of a magnetic TI sandwich heterostructure device, we demonstrate that the predominant dissipation mechanism in thick QAH insulators can switch between nonchiral edge states and residual bulk states in different magnetic-field regimes. The interactions between bulk states, chiral edge states, and nonchiral edge states are also investigated. Our Letter provides a way to distinguish between the dissipation arising from the residual bulk states and nonchiral edge states, which is crucial for achieving true dissipationless transport in QAH insulators and for providing deeper insights into QAH-related phenomena.

This work demonstrates significant line narrowing of a surface multipole plasmon (MP) by modifying the surface electronic wave function with two-dimensional materials (2DMs): graphene and hexagonal boron nitride. This is found in an optical reflectivity of alkali atoms (Cs or K) on an Ir(111) surface covered with the 2DMs. The reduction in reflectivity induced by deposition of the alkali atoms becomes as large as 20% at $\sim 2\mathrm{eV}$, which is ascribed to a MP of a composite of alkali/2DM/alkali/Ir multilayer structure. The linewidth of the MP band becomes as narrow as 0.2 eV by the presence of the 2DM between the two alkali layers. A numerical simulation by time-dependent density functional theory with a jellium model reveals that the density of states of the surface localized state is sharpened remarkably by the 2DMs that decouple the outermost alkali layer from the Ir bulk. Consequently, a local field enhancement of an order of ${10}^5$ is achieved by ultimate confinement of the MP within the outermost alkali layer. This work leads to a novel strategy for reducing plasmon dissipation in an atomically thin layer via atomic scale modification of surface structure.

Using a minimal algebraic model for the thermodynamics of binary rod-polymer mixtures, we provide evidence for a quintuple phase equilibrium; an observation that seems to be at odds with the Gibbs phase rule for two-component systems. Our model is based on equations of state for the relevant liquid crystal phases that are in quantitative agreement with computer simulations. We argue that the appearance of a quintuple equilibrium, involving an isotropic fluid, a nematic and smectic liquid crystal, and two solid phases, can be reconciled with a generalized Gibbs phase rule in which the two intrinsic length scales of the athermal colloid-polymer mixture act as additional field variables.

We report on a search for dark matter axion conversion photons from the magnetosphere of the Galactic Center magnetar PSR J1745-2900 using spectra obtained from the Karl G. Jansky Very Large Array (the National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.). No significant spectral features are detected. Using a hybrid model for PSR J1745-2900 and canonical assumptions about the dark matter density profile, we exclude axion models with axion-photon coupling $g_{a\gamma \gamma }>6–34\times {10}^{-12}{\mathrm{GeV}}^{-1}$ with 95% confidence over the mass ranges 4.2–8.4, 18.6–26.9, 33.0–41.4, 53.7–62.1, and $126.0–159.3\mu \mathrm{eV}$. If there is a dark matter cusp, the limits reduce to $g_{a\gamma \gamma }>6–34\times {10}^{-14}{\mathrm{GeV}}^{-1}$, which overlap some axion models for the observed mass ranges $>33\mu \mathrm{eV}$. These limits may be improved by modeling the stimulated emission that can boost the axion-photon conversion process.

We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010–2015. Assuming standard oscillations, the astrophysical neutrinos in this dedicated cascade sample are dominated ($\sim 90\%$) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be $\gamma =2.53\pm 0.07$ and a flux normalization for each neutrino flavor of ${\varphi }_{\text{astro}}=1.66_{-0.27}^{+0.25}$ at $E_0=100\mathrm{TeV}$, in agreement with IceCube’s complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices $\gamma \le 2.28$ at $\ge 3\sigma$ significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below $\sim 100\mathrm{TeV}$ compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies ($p$ value $\ge 0.06$). The sizable and smooth flux measured below $\sim 100\mathrm{TeV}$ remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.

We establish the existence of a far-from-equilibrium attractor in weakly coupled gauge theory undergoing one-dimensional Bjorken expansion. We demonstrate that the resulting far-from-equilibrium evolution is insensitive to certain features of the initial condition, including both the initial momentum-space anisotropy and initial occupancy. We find that this insensitivity extends beyond the energy-momentum tensor to the detailed form of the one-particle distribution function. Based on our results, we assess different procedures for reconstructing the full one-particle distribution function from the energy-momentum tensor along the attractor and discuss implications for the freeze-out procedure used in the phenomenological analysis of ultrarelativistic nuclear collisions.

This work provides the fundamental theoretical framework for molecular cavity quantum electrodynamics by resolving the gauge ambiguities between the Coulomb gauge and the dipole gauge Hamiltonians under the electronic state truncation. We conjecture that such ambiguity arises because not all operators are consistently constrained in the same truncated electronic subspace for both gauges. We resolve this ambiguity by constructing a unitary transformation operator that properly constrains all light-matter interaction terms in the same subspace. We further derive an equivalent and yet convenient expression for the Coulomb gauge Hamiltonian under the truncated subspace. We finally provide the analytical and numerical results of a model molecular system coupled to the cavity to demonstrate the validity of our theory.

We consider exciton polaritons in a zigzag chain of coupled elliptical micropillars subjected to incoherent excitation. The driven-dissipative nature of the system along with the naturally present polarization splitting inside the pillars gives rise to nonreciprocal dynamics, which eventually leads to the non-Hermitian skin effect, where all the modes of the system collapse to one edge. As a result, the polaritons propagate only in one direction along the chain, independent of the excitation position, and the propagation in the opposite direction is suppressed. The system shows robustness against disorder and, using the bistable nature of polaritons to encode information, we show one-way information transfer. This paves the way for compact and robust feedback-free one-dimensional polariton transmission channels without the need for external magnetic field, which are compatible with proposals for polaritonic circuits.

The cohesive zone is the elusive region in which material fracture takes place. Here, the putatively singular stresses at a crack’s tip are regularized. We present experiments, performed on PMMA, in which we visualize the cohesive zone of frictional ruptures as they propagate. Identical to shear cracks, these ruptures range from slow velocities to nearly the limiting speeds of cracks. We reveal that the cohesive zone is a dynamic quantity; its spatial form undergoes a sharp transition between distinct phases at a critical velocity. The structure of these phases provides an important window into material properties under the extreme conditions that occur during fracture.

It has been recently revealed that strontium titanate (${\mathrm{SrTiO}}_3$) displays persistent photoconductivity with unique characteristics: it occurs at room temperature and lasts over a very long period of time. Illumination of ${\mathrm{SrTiO}}_3$ crystals at room temperature with sub-band-gap light reduces the electrical resistance by three orders of magnitude and persists for weeks or longer [Tarun et al., Phys. Rev. Lett. 111, 187403 (2013)]. Experiments indicate that oxygen vacancy and hydrogen play important roles, yet the microscopic mechanism responsible for this remarkable effect has remained unidentified. Using hybrid density functional theory calculations we show that an instability associated with substitutional hydrogen ${\mathrm{H}}_{\mathrm{O}}^{+}$ under illumination, which becomes doubly ionized and leaves the oxygen site, can explain the experimental observations. ${\mathrm{H}}_{\mathrm{O}}$ then turns into an interstitial hydrogen and an oxygen vacancy, leading to excess carriers in the conduction band. This phenomenon is not exclusive to ${\mathrm{SrTiO}}_3$, but it is also predicted to occur in other oxides. Interestingly, this phenomenon represents an elegant way of proving the existence of hydrogen substituting on an oxygen site (${\mathrm{H}}_{\mathrm{O}}$), forming an interesting, and rarely observed, type of three-center, two-electron bond.

We present wave transport experiments in hyperuniform disordered arrays of cylinders with high dielectric permittivity. Using microwaves, we show that the same material can display transparency, photon diffusion, Anderson localization, or a full band gap, depending on the frequency $\nu$ of the electromagnetic wave. Interestingly, we find a second weaker band gap, which appears to be related to the second peak of the structure factor. Our results emphasize the importance of spatial correlations on different length scales for the formation of photonic band gaps.

In order to confine waves beyond the diffraction limit, advances in fabrication techniques have enabled subwavelength structuring of matter, achieving near-field control of light and other types of waves. The price is often expensive fabrication needs and the irreversibility of device functionality, as well as the introduction of impurities, a major contributor to losses. In this Letter, we propose temporal inhomogeneities, such as a periodic drive in the electromagnetic properties of a surface which supports guided modes, as an alternative route for the coupling of propagating waves to evanescent modes across the light line, thus circumventing the need for subwavelength fabrication, and achieving the temporal counterpart of the classical Wood anomaly. We show analytically and numerically how this concept is valid for any material platform and at any frequency, and propose and model a realistic experiment in graphene to couple terahertz radiation to plasmons with unit efficiency, demonstrating that time modulation of material properties could be a tunable, lower-loss and fast-switchable alternative to the subwavelength structuring of matter for near-field wave control.