The precise measurement of transition frequencies in cold, trapped molecules has applications in fundamental physics, and extremely high accuracies are desirable. We determine suitable candidates by considering the simplest molecules with a single electron, for which the external-field shift corrections can be calculated theoretically with high precision. Our calculations show that ${{\mathrm{H}}_2}^{+}$ exhibits particular transitions whose fractional systematic uncertainties may be reduced to $5\times {10}^{-17}$ at room temperature. We also generalize the method of composite frequencies, introducing tailored linear combinations of individual transition frequencies that are free of the major systematic shifts, independent of the strength of the external perturbing fields. By applying this technique, the uncertainty of the composite frequency is reduced compared to what is achievable with a single transition, e.g., to the ${10}^{-18}$ range for ${\text{HD}}^{+}$. Thus, these molecules are of metrological relevance for future studies.

We report the direct observation of the three-dimensional (3D) Dirac semimetal phase in cadmium arsenide (${\mathrm{Cd}}_3{\mathrm{As}}_2$) by means of angle-resolved photoemission spectroscopy. We identify two momentum regions where electronic states that strongly disperse in all directions form narrow conelike structures, and thus prove the existence of the long sought 3D Dirac points. This electronic structure naturally explains why ${\mathrm{Cd}}_3{\mathrm{As}}_2$ has one of the highest known bulk electron mobilities. This realization of a 3D Dirac semimetal in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ not only opens a direct path to a wide spectrum of applications, but also offers a robust platform for engineering topologically nontrivial phases including Weyl semimetals and quantum spin Hall systems.

The plasma which forms inside of a micron-sized sonoluminescing bubble in water for under a nanosecond has been probed with 3 ns long laser pulses. A comparison of the response to 532 and 1064 nm light indicates that the plasma number density is about $2\times {10}^{21}{\mathrm{cm}}^{-3}$ and that transport properties are dominated by strong screening and correlation effects. The spherical shape, well-defined atomic density, and blackbody temperature make the sonoluminescing plasma a test bed for theories of strongly coupled plasmas. The plasma in this experiment distinguishes between competing theories of strong, intermediate, and weak effective screening.

In ideal topological insulator (TI) films the bulk state, which is supposed to be insulating, should not provide any electric coupling between the two metallic surfaces. However, transport studies on existing TI films show that the topological states on opposite surfaces are electrically tied to each other at thicknesses far greater than the direct coupling limit where the surface wave functions overlap. Here, we show that as the conducting bulk channels are suppressed, the parasitic coupling effect diminishes, and the decoupled surface channels emerge as expected for ideal TIs. In ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ thin films with fully suppressed bulk states, the two surfaces, which are directly coupled below $\sim 10\mathrm{QL}$, become gradually isolated with increasing thickness and are completely decoupled beyond $\sim 20\mathrm{QL}$. On such a platform, it is now feasible to implement transport devices whose functionality relies on accessing the individual surface layers without any deleterious coupling effects.

We report the observation of the spin Peltier effect (SPE) in the ferrimagnetic insulator yttrium iron garnet (YIG), i.e., a heat current generated by a spin current flowing through a platinum $(\mathrm{Pt})|\mathrm{YIG}$ interface. The effect can be explained by the spin transfer torque that transforms the spin current in the Pt into a magnon current in the YIG. Via magnon-phonon interactions the magnetic fluctuations modulate the phonon temperature that is detected by a thermopile close to the interface. By finite-element modeling we verify the reciprocity between the spin Peltier and spin Seebeck effect. The observed strong coupling between thermal magnons and phonons in YIG is attractive for nanoscale cooling techniques.

We report a new class of tunable and switchable acoustic metamaterials comprising resonating units dispersed into an elastic matrix. Each resonator consists of a metallic core connected to the elastomeric matrix through elastic beams, whose buckling is intentionally exploited as a novel and effective approach to control the propagation of elastic waves. We first use numerical analysis to show the evolution of the locally resonant band gap, fully accounting for the effect of nonlinear pre-deformation. Then, we experimentally measure the transmission of vibrations as a function of the applied loading in a finite-size sample and find excellent agreement with our numerical predictions. The proposed concept expands the ability of existing acoustic metamaterials by enabling tunability over a wide range of frequencies. Furthermore, we demonstrate that in our system the deformation can be exploited to turn on or off the band gap, opening avenues for the design of adaptive switches.

The recent detection of $B$ modes by the BICEP2 experiment has nontrivial implications for axion dark matter implied by combining the tensor interpretation with isocurvature constraints from Planck observations. In this Letter the measurement is taken as fact, and its implications considered, though further experimental verification is required. In the simplest inflation models, $r=0.2$ implies $H_I=1.1\times {10}^{14}\mathrm{GeV}$. If the axion decay constant $f_a<H_I/2\pi$, constraints on the dark matter (DM) abundance alone rule out the QCD axion as DM for $m_a\lesssim 52{\chi }^{6/7}\mu \mathrm{eV}$ (where $\chi >1$ accounts for theoretical uncertainty). If $f_a>H_I/2\pi$ then vacuum fluctuations of the axion field place conflicting demands on axion DM: isocurvature constraints require a DM abundance which is too small to be reached when the backreaction of fluctuations is included. High-$f_a$ QCD axions are thus ruled out. Constraints on axionlike particles, as a function of their mass and DM fraction, are also considered. For heavy axions with $m_a\gtrsim {10}^{-22}\mathrm{eV}$ we find ${\mathrm{\Omega }}_a/{\mathrm{\Omega }}_d\lesssim {10}^{-3}$, with stronger constraints on heavier axions. Lighter axions, however, are allowed and (inflationary) model-independent constraints from the CMB temperature power spectrum and large scale structure are stronger than those implied by tensor modes.

The properties of axions that constitute 100% of cold dark matter (CDM) depend on the tensor-to-scalar ratio $r$ at the end of inflation. If $r=0.20_{-0.05}^{+0.07}$ as reported by the BICEP2 Collaboration, then “half” of the CDM axion parameter space is ruled out. Namely, in the context of single-field slow-roll inflation, for axions to be 100% of the CDM, the Peccei-Quinn symmetry must be broken after the end of inflation, so that axion nonadiabatic primordial fluctuations are compatible with observational constraints. The cosmic axion density is then independent of the tensor-to-scalar ratio $r$, and the axion mass is expected to be in a narrow range that, however, depends on the cosmological model before primordial nucleosynthesis. In the standard Lambda CDM cosmology, the CDM axion mass range is $m_a=(71\pm 2\mu \mathrm{eV})({\alpha }^{\text{dec}}+1{)}^{6/7}$, where ${\alpha }^{\text{dec}}$ is the fractional contribution to the cosmic axion density from decays of axionic strings and walls.

We discuss the impact of recent high-statistics Relativistic Heavy Ion Collider data on the determination of the gluon polarization in the proton in the context of a global QCD analysis of polarized parton distributions. We find evidence for a nonvanishing polarization of gluons in the region of momentum fraction and at the scales mostly probed by the data. Although information from low momentum fractions is presently lacking, this finding is suggestive of a significant contribution of gluon spin to the proton spin, thereby limiting the amount of orbital angular momentum required to balance the proton spin budget.

We implement the squeezing operation as a genuine quantum gate, deterministically and reversibly acting “online” upon an input state no longer restricted to the set of Gaussian states. More specifically, by applying an efficient and robust squeezing operation for the first time to non-Gaussian states, we demonstrate a two-way conversion between a particlelike single-photon state and a wavelike superposition of coherent states. Our squeezing gate is reliable enough to preserve the negativities of the corresponding Wigner functions. This demonstration represents an important and necessary step towards hybridizing discrete and continuous quantum protocols.

We scrutinize the concept of integrable nonlinear communication channels, resurrecting and extending the idea of eigenvalue communications in a novel context of nonsoliton coherent optical communications. Using the integrable nonlinear Schrödinger equation as a channel model, we introduce a new approach—the nonlinear inverse synthesis method—for digital signal processing based on encoding the information directly onto the nonlinear signal spectrum. The latter evolves trivially and linearly along the transmission line, thus, providing an effective eigenvalue division multiplexing with no nonlinear channel cross talk. The general approach is illustrated with a coherent optical orthogonal frequency division multiplexing transmission format. We show how the strategy based upon the inverse scattering transform method can be geared for the creation of new efficient coding and modulation standards for the nonlinear channel.

Electrostatic interactions play an important role in numerous self-assembly phenomena, including colloidal aggregation. Although colloids typically have a dielectric constant that differs from the surrounding solvent, the effective interactions that arise from inhomogeneous polarization charge distributions are generally neglected in theoretical and computational studies. We introduce an efficient technique to resolve polarization charges in dynamical dielectric geometries, and demonstrate that dielectric effects qualitatively alter the predicted self-assembled structures, with surprising colloidal strings arising from many-body effects.

We present the results of a search for gravitational waves associated with 223 $\gamma$-ray bursts (GRBs) detected by the InterPlanetary Network (IPN) in 2005–2010 during LIGO’s fifth and sixth science runs and Virgo’s first, second, and third science runs. The IPN satellites provide accurate times of the bursts and sky localizations that vary significantly from degree scale to hundreds of square degrees. We search for both a well-modeled binary coalescence signal, the favored progenitor model for short GRBs, and for generic, unmodeled gravitational wave bursts. Both searches use the event time and sky localization to improve the gravitational wave search sensitivity as compared to corresponding all-time, all-sky searches. We find no evidence of a gravitational wave signal associated with any of the IPN GRBs in the sample, nor do we find evidence for a population of weak gravitational wave signals associated with the GRBs. For all IPN-detected GRBs, for which a sufficient duration of quality gravitational wave data are available, we place lower bounds on the distance to the source in accordance with an optimistic assumption of gravitational wave emission energy of $10^{-2}{M}_{\odot }{c}^2$ at 150 Hz, and find a median of 13 Mpc. For the 27 short-hard GRBs we place 90% confidence exclusion distances to two source models: a binary neutron star coalescence, with a median distance of 12 Mpc, or the coalescence of a neutron star and black hole, with a median distance of 22 Mpc. Finally, we combine this search with previously published results to provide a population statement for GRB searches in first-generation LIGO and Virgo gravitational wave detectors and a resulting examination of prospects for the advanced gravitational wave detectors.

We report a measurement of a new high spin $J^{\pi }=5^{-}$ state at 22.4(2) MeV in ${}^{12}\mathrm{C}$ which fits very well to the predicted (ground state) rotational band of an oblate equilateral triangular spinning top with a ${\mathcal{D}}_{3h}$ symmetry characterized by the sequence $0^{+}$, $2^{+}$, $3^{-}$, $4^{\pm }$, $5^{-}$ with almost degenerate $4^{+}$ and $4^{-}$ (parity doublet) states. Such a ${\mathcal{D}}_{3h}$ symmetry was observed in triatomic molecules, and it is observed here for the first time in nuclear physics. We discuss a classification of other rotation-vibration bands in ${}^{12}\mathrm{C}$ such as the ($0^{+}$) Hoyle band and the ($1^{-}$) bending mode band and suggest measurements in search of the predicted (“missing”) states that may shed new light on clustering in ${}^{12}\mathrm{C}$ and light nuclei. In particular, the observation (or nonobservation) of the predicted (“missing”) states in the Hoyle band will allow us to conclude the geometrical arrangement of the three alpha particles composing the Hoyle state at 7.654 MeV in ${}^{12}\mathrm{C}$.

We present a simple empirical function for the average density profile of cosmic voids, identified via the watershed technique in $\mathrm{\Lambda }\mathrm{CDM}$ $N$-body simulations. This function is universal across void size and redshift, accurately describing a large radial range of scales around void centers with only two free parameters. In analogy to halo density profiles, these parameters describe the scale radius and the central density of voids. While we initially start with a more general four-parameter model, we find two of its parameters to be redundant, as they follow linear trends with the scale radius in two distinct regimes of the void sample, separated by its compensation scale. Assuming linear theory, we derive an analytic formula for the velocity profile of voids and find an excellent agreement with the numerical data as well. In our companion paper [Sutter et al., arXiv:1309.5087 [Mon. Not. R. Astron. Soc. (to be published)]], the presented density profile is shown to be universal even across tracer type, properly describing voids defined in halo and galaxy distributions of varying sparsity, allowing us to relate various void populations by simple rescalings. This provides a powerful framework to match theory and simulations with observational data, opening up promising perspectives to constrain competing models of cosmology and gravity.

The fundamental rotational transition $J=1\leftarrow 0$ of the anion ${\mathrm{OH}}^{-}$ has been measured by cooling mass-selected ${\mathrm{OH}}^{-}$ ions to 10 K in a 22-pole ion trap and applying a novel rotational-rovibrational two-photon scheme. A transition frequency of $(1\hspace{0.17em}\hspace{0.17em}123\hspace{0.17em}101.0410\pm 0.0014)\mathrm{MHz}$ was obtained with so far unprecedented accuracy. The general application of the presented action-spectroscopy scheme to other anions and cations is discussed.

The more information a measurement provides about a quantum system’s position statistics, the less information a subsequent measurement can provide about the system’s momentum statistics. This information trade-off is embodied in the entropic formulation of the uncertainty principle. Traditionally, uncertainly relations correspond to resolution limits; increasing a detector’s position sensitivity decreases its momentum sensitivity and vice versa. However, this is not required in general; for example, position information can instead be extracted at the cost of noise in momentum. Using random, partial projections in position followed by strong measurements in momentum, we efficiently determine the transverse-position and transverse-momentum distributions of an unknown optical field with a single set of measurements. The momentum distribution is directly imaged, while the position distribution is recovered using compressive sensing. At no point do we violate uncertainty relations; rather, we economize the use of information we obtain.

We observe two consecutive heteronuclear Efimov resonances in an ultracold Li-Cs mixture by measuring three-body loss coefficients as a function of magnetic field near a Feshbach resonance. The first resonance is detected at a scattering length of $a_{-}^{(0)}=-320(10)a_0$, corresponding to $\sim 7(\sim 3)$ times the Li-Cs (Cs-Cs) van der Waals range. The second resonance appears at $5.8(1.0)a_{-}^{(0)}$, close to the unitarity-limited regime at the sample temperature of 450 nK. Indication of a third resonance is found in the atom loss spectra. The scaling of the resonance positions is close to the predicted universal scaling value of 4.9 for zero temperature. Deviations from universality might be caused by finite-range and temperature effects, as well as magnetic field–dependent Cs-Cs interactions.

Bilayer graphene is a highly promising material for electronic and optoelectronic applications since it is supporting massive Dirac fermions with a tunable band gap. However, no consistent picture of the gap’s effect on the optical and transport behavior has emerged so far, and it has been proposed that the insulating nature of the gap could be compromised by unavoidable structural defects, by topological in-gap states, or that the electronic structure could be altogether changed by many-body effects. Here, we directly follow the excited carriers in bilayer graphene on a femtosecond time scale, using ultrafast time- and angle-resolved photoemission. We find a behavior consistent with a single-particle band gap. Compared to monolayer graphene, the existence of this band gap leads to an increased carrier lifetime in the minimum of the lowest conduction band. This is in sharp contrast to the second substate of the conduction band, in which the excited electrons decay through fast, phonon-assisted interband transitions.

A new scheme of making crystalline undulators was recently proposed and investigated theoretically by Andriy Kostyuk, concluding that a new type of crystalline undulator would be not only viable, but better than the previous scheme. This article describes the first experimental measurement of such a crystalline undulator, produced by using ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$-graded composition and measured at the Mainzer Microtron facility at beam energies of 600 and 855 MeV. We also present theoretical models developed to compare with the experimental data.