We report on nanoscale strain gradients in ferroelectric ${\mathrm{HoMnO}}_3$ epitaxial thin films, resulting in a giant flexoelectric effect. Using grazing-incidence in-plane x-ray diffraction, we measured strain gradients in the films, which were 6 or 7 orders of magnitude larger than typical values reported for bulk oxides. The combination of transmission electron microscopy, electrical measurements, and electrostatic calculations showed that flexoelectricity provides a means of tuning the physical properties of ferroelectric epitaxial thin films, such as domain configurations and hysteresis curves.

The interaction of a quantum system with the environment leads to the so-called quantum decoherence. Beyond its fundamental significance, the understanding and the possible control of this dynamics in various scenarios is a key element for mastering quantum information processing. Here we report the quantitative probing of what can be called the quantum decoherence of detectors, a process reminiscent of the decoherence of quantum states in the presence of coupling with a reservoir. We demonstrate how the quantum features of two single-photon counters vanish under the influence of a noisy environment. We thereby experimentally witness the transition between the full-quantum operation of the measurement device to the "semi-classical regime", described by a positive Wigner function. The exact border between these two regimes is explicitely determined and measured experimentally.

A comparison of the relative yields of ${\rm Y}$ resonances in the ${\mu }^{+}{\mu }^{-}$ decay channel in Pb-Pb and $pp$ collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above $4\mathrm{GeV}/c$ and pseudorapidity below 2.4, the double ratio of the ${\rm Y}(2S)$ and ${\rm Y}(3S)$ excited states to the ${\rm Y}(1S)$ ground state in Pb-Pb and $pp$ collisions, $[{\rm Y}(2S+3S)/{\rm Y}(1S){]}_{\mathrm{Pb}\mathrm{\text{−}}\mathrm{Pb}}/[{\rm Y}(2S+3S)/{\rm Y}(1S){]}_{pp}$, is found to be ${0.31}_{-0.15}^{+0.19}(\mathrm{stat})\pm 0.03(\mathrm{syst})$. The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%.

Surface states—the electronic states emerging as a solid material terminates at a surface—are usually vulnerable to contaminations and defects. The robust topological surface state(s) (TSS) on the three-dimensional topological insulators provide a perfect platform for exploiting surface states in less stringent environments. Employing first-principles density functional theory calculations, we demonstrate that the TSS can play a vital role in facilitating surface reactions by serving as an effective electron bath. We use CO oxidation on gold-covered ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ as a prototype example, and show that the robust TSS can significantly enhance the adsorption energy of both CO and ${\mathrm{O}}_2$ molecules, by promoting different directions of static electron transfer. The concept of TSS as an electron bath may lead to new design principles beyond the conventional $d$-band theory of heterogeneous catalysis.

Recently, the steady sedimentation profile of a dilute suspension of chemically powered colloids was studied experimentally [J. Palacci et al., Phys. Rev. Lett. 105, 088304 (2010)]. It was found that the sedimentation length increases quadratically with the swimming speed of the active Brownian particles. Here we investigate theoretically the sedimentation of self-propelled particles undergoing translational and rotational diffusion. We find that the measured increase of the sedimentation length is coupled to a partial alignment of the suspension with the mean swimming direction oriented against the gravitational field. We suggest realistic parameter values to observe this polar order. Furthermore, we find that the dynamics of the active suspension can be derived from a generalized free energy functional.

Experimental evidence for the correlated two-electron one-photon transitions ($1s^{-2}\to 2s^{-1}2p^{-1}$) following single-photon $K$-shell double ionization is reported. The double $K$-shell vacancy states in solid Mg, Al, and Si were produced by means of monochromatized synchrotron radiation, and the two-electron one-photon radiative transitions were observed by using a wavelength dispersive spectrometer. The two-electron one-photon transition energies and the branching ratios of the radiative one-electron to two-electron transitions were determined and compared to available perturbation theory predictions and configuration interaction calculations.

We present a device-independent protocol to test if a given black-box measurement device is entangled, that is, has entangled eigenstates. Our scheme involves three parties and is inspired by entanglement swapping; the test uses the Clauser-Horne-Shimony-Holt Bell inequality, checked between each pair of parties. In the case where all particles are qubits, we characterize quantitatively the deviation of the measurement device from a perfect Bell-state measurement.

Room-temperature, easy-to-operate quantum memories are essential building blocks for future long distance quantum information networks operating on an intercontinental scale, because devices like quantum repeaters, based on quantum memories, will have to be deployed in potentially remote, inaccessible locations. Here we demonstrate controllable, broadband and efficient storage and retrieval of weak coherent light pulses at the single-photon level in warm atomic cesium vapor using the robust far off-resonant Raman memory scheme. We show that the unconditional noise floor of this technically simple quantum memory is low enough to operate in the quantum regime, even in a room-temperature environment.

Ferromagnetism is usually considered to be incompatible with conventional superconductivity, as it destroys the singlet correlations responsible for the pairing interaction. Superconductivity and ferromagnetism are known to coexist in only a few bulk rare-earth materials. Here we report evidence for their coexistence in a two-dimensional system: the interface between two bulk insulators, ${\mathrm{LaAlO}}_3$ (LAO) and ${\mathrm{SrTiO}}_3$ (STO), a system that has been studied intensively recently. Magnetoresistance, Hall, and electric-field dependence measurements suggest that there are two distinct bands of charge carriers that contribute to the interface conductivity. The sensitivity of properties of the interface to an electric field makes this a fascinating system for the study of the interplay between superconductivity and magnetism.

We examine the relevance of magnetoelastic coupling to describe the complex magnetic and structural behavior of the different classes of the iron superconductors. We model the system as a two-dimensional metal whose magnetic excitations interact with the distortions of the underlying square lattice. Going beyond the mean field, we find that quantum fluctuation effects can explain two unusual features of these materials that have attracted considerable attention: first, why iron telluride orders magnetically at a non-nesting wave vector $(\pi /2,\pi /2)$ and not at the nesting wave vector $(\pi ,0)$ as in the iron arsenides, even though the nominal band structures of both these systems are similar, and second, why the $(\pi ,0)$ magnetic transition in the iron arsenides is often preceded by an orthorhombic structural transition. These are robust properties of the model, independent of microscopic details, and they emphasize the importance of the magnetoelastic interaction.

The Copernican principle, a cornerstone of modern cosmology, remains largely unproven at the Gpc radial scale and above. Here will show that violations of this type will inevitably cause a first order anisotropic kinetic Sunyaev-Zel’dovich effect. If large scale radial inhomogeneities have an amplitude large enough to explain the “dark energy” phenomena, the induced kinetic Sunyaev-Zel’dovich power spectrum will be much larger than the Atacama Cosmology Telescope and/or South Pole Telescope upper limit. This single test confirms the Copernican principle and rules out the adiabatic void model as a viable alternative to dark energy.

Moving micron-scale objects are strongly coupled to each other by hydrodynamic interactions. The strength of this coupling decays with the inverse particle separation when the two objects are sufficiently far apart. It has been recently demonstrated that the reduced dimensionality of a thin fluid layer gives rise to longer-ranged, logarithmic coupling. Using holographic tweezers we show that microrods display both behaviors interacting like point particles in three dimensions at large distances and like point particles in two dimensions for distances shorter then their length. We derive a simple analytical expression that fits our data remarkably well and further validate it with finite element analysis.

The T2K experiment observes indications of ${\nu }_{\mu }\to {\nu }_e$ appearance in data accumulated with $1.43\times {10}^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|\Delta m_{23}^2|=2.4\times {10}^{-3}{\mathrm{eV}}^2$, ${sin}^{2}2{\theta }_{23}=1$ and ${sin}^{2}2{\theta }_{13}=0$, the expected number of such events is $1.5\pm 0.3(\mathrm{syst})$. Under this hypothesis, the probability to observe six or more candidate events is $7\times {10}^{-3}$, equivalent to $2.5\sigma$ significance. At 90% C.L., the data are consistent with $0.03(0.04)<{sin}^{2}2{\theta }_{13}<0.28(0.34)$ for ${\delta }_{CP}=0$ and a normal (inverted) hierarchy.

We develop a graphical method for computing the virial expansion coefficients for a nonrelativistic quantum field theory. As an example we compute the third virial coefficient $b_3$ for unitary fermions, a nonperturbative system. By calculating several graphs and performing an extrapolation, we arrive at $b_3=-0.2930$, within 0.7% of a recent computation $b_3=-0.29095295$ by Liu, Hu, and Drummond, which involved summing 10 000 energy levels for three unitary fermions in a harmonic trap.

Enhancement of the ion temperature and fusion yield has been observed in magnetized laser-driven inertial confinement fusion implosions on the OMEGA Laser Facility. A spherical CH target with a 10 atm ${\mathrm{D}}_2$ gas fill was imploded in a polar-drive configuration. A magnetic field of 80 kG was embedded in the target and was subsequently trapped and compressed by the imploding conductive plasma. As a result of the hot-spot magnetization, the electron radial heat losses were suppressed and the observed ion temperature and neutron yield were enhanced by 15% and 30%, respectively.

We study structures which can bear loads, “bridges”, in particulate packings. To investigate the relationship between bridges and gravity, we experimentally determine bridge statistics in colloidal packings. We vary the effective magnitude and direction of gravity, volume fraction, and interactions, and find that the bridge size distributions depend only on the mean number of neighbors. We identify a universal distribution, in agreement with simulation results for granulars, suggesting that applied loads merely exploit preexisting bridges, which are inherent in dense packings.

Scalability and coherence are two essential requirements for the experimental implementation of quantum information and quantum computing. Here, we report a breakthrough toward scalability: the simultaneous generation of a record 15 quadripartite entangled cluster states over 60 consecutive cavity modes ($Q$ modes), in the optical frequency comb of a single optical parametric oscillator. The amount of observed entanglement was constant over the 60 $Q$ modes, thereby proving the intrinsic scalability of this system. The number of observable $Q$ modes was restricted by technical limitations, and we conservatively estimate the actual number of similar clusters to be at least 3 times larger. This result paves the way to the realization of large entangled states for scalable quantum information and quantum computing.

We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co $L_3$ edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.

The atomic and electronic structures of ErAs nanoparticles embedded within a GaAs matrix are examined via cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/XSTS). The local density of states (LDOS) exhibits a finite minimum at the Fermi level demonstrating that the nanoparticles remain semimetallic despite the predictions of previous models of quantum confinement in ErAs. We also use XSTS to measure changes in the LDOS across the $\mathrm{ErAs}/\mathrm{GaAs}$ interface and propose that the interface atomic structure results in electronic states that prevent the opening of a band gap.

Charge-changing cross sections ${\sigma }_{\mathrm{cc}}$ of stable and unstable nuclei (${}^{9–11}\mathrm{Be}$, ${}^{14–16}\mathrm{C}$, and ${}^{16–18}\mathrm{O}$) on a carbon target were investigated at $300\mathrm{MeV}/\mathrm{nucleon}$. A phenomenological analysis based on the Glauber theory indicates an approximate, but universal, scaling of ${\sigma }_{\mathrm{cc}}$ over a wide range of $A/Z$. This allows the determination of the density distributions of protons tightly bound in the nuclei. An application to ${}^{16}\mathrm{C}$, which is considered to be an anomalously deformed nucleus, indicates a systematic evolution of proton root-mean-square radii and has revealed for the first time a neutron skin effect in carbon isotopes. Being complementary to isotope-shift and electron-scattering experiments, the present method can open up a new approach to explore the structure of exotic nuclei.