A simple quantum-defect model gives analytic expressions for the complex scattering length and threshold collision rates of ultracold molecules. If the probability of reaction in the short-range part of the collision is high, the model gives universal rate constants for $s$- and $p$-wave collisions that are independent of short-range dynamics. This model explains the magnitudes of the recently measured rate constants for collisions of two ultracold ${}^{40}\mathrm{K}{}^{87}\mathrm{Rb}$ molecules, or an ultracold ${}^{40}\mathrm{K}$ atom with the ${}^{40}\mathrm{K}{}^{87}\mathrm{Rb}$ molecule [S. Ospelkaus et al., Science 327, 853 (2010)].

We present results from numerical solution of the Einstein field equations describing the head-on collision of two solitons boosted to ultrarelativistic energies. We show, for the first time, that at sufficiently high energies the collision leads to black hole formation, consistent with hoop-conjecture arguments. This implies that the nonlinear gravitational interaction between the kinetic energy of the solitons causes gravitational collapse, and that arguments for black hole formation in super-Planck scale particle collisions are robust.

Oxygen is the only elemental molecule which carries an electronic magnetic moment. As a consequence, the different solid phases encountered on cooling show various degrees of magnetic order, and similar behavior is expected under compression. Here we present neutron diffraction data which reveal the magnetic ordering under high pressure in the $\delta$ (“orange”) phase, i.e., in the range 6–8 GPa and 20–240 K. We show that $\delta \mathrm{\text{−}}{\mathrm{O}}_2$ contains in total three different magnetic structures, all of them being antiferromagnetic and differing in the stacking sequence of ${\mathrm{O}}_2$ sheets along the $c$ axis. This structural diversity can be explained by the quasi-two-dimensional nature of $\delta \mathrm{\text{−}}{\mathrm{O}}_2$ and the strong orientation dependence of the magnetic exchange interaction between ${\mathrm{O}}_2$ molecules. The results show that $\delta \mathrm{\text{−}}{\mathrm{O}}_2$ is a room temperature antiferromagnet.

Using single-molecule fluorescence imaging, we track Brownian motion perpendicular to the contour of tightly entangled F-actin filaments and extract the confining potential. The chain localization presents a small-displacement Hookean regime followed by a large amplitude regime where the effective restoring force is independent of displacement. The implied heterogeneity characterized by a distribution of tube width is modeled.

We compute the three-loop corrections to the potential of two heavy quarks. In particular, we consider in this Letter the purely gluonic contribution which provides, in combination with our previous fermion corrections, the complete answer at three loops.

We compute the purely gluonic contribution to the static QCD potential at three-loop order. This completes computation of the static potential at this order.

High-temperature cuprate superconductors exhibit extremely local nanoscale phenomena and strong sensitivity to doping. While other experiments have looked at nanoscale interfaces between layers of different dopings, we focus on the interplay between naturally inhomogeneous nanoscale regions. Using scanning tunneling microscopy to carefully track the same region of the sample as a function of temperature, we show that regions with weak superconductivity can persist to elevated temperatures if bordered by regions of strong superconductivity. This suggests that it may be possible to increase the maximum possible transition temperature by controlling the distribution of dopants.

We theoretically investigated the nonadiabatic couplings between optically induced $\pi$-electron rotations and molecular vibrations in a chiral aromatic molecule irradiated by a nonhelical, linearly polarized laser pulse. The results of wave packet dynamics simulation show that the vibrational amplitudes strongly depend on the initial rotation direction, clockwise or counterclockwise, which is controlled by the polarization direction of the incident pulse. This suggests that attosecond $\pi$-electron rotations can be observed by spectroscopic detection of femtosecond molecular vibrations.

We present the realization of a cavity quantum electrodynamics setup in which photons of strongly different lifetimes are engineered in different harmonic modes of the same cavity. We achieve this in a superconducting transmission line resonator with superconducting qubits coupled to the different modes. One cavity mode is strongly coupled to a detection line for qubit state readout, while a second long lifetime mode is used for photon storage and coherent quantum operations. We demonstrate sideband-based measurement of photon coherence, generation of $n$ photon Fock states and the scaling of the sideband Rabi frequency with $\sqrt{n}$ using a scheme that may be extended to realize sideband-based two-qubit logic gates.

We present a model of weak scale dark matter (DM) where the thermal DM density is set by the lepton asymmetry due to the presence of higher dimension lepton violating operators. In these models there is generically a separation between the annihilation cross section responsible for the relic abundance (through lepton violating operators) and the annihilation cross section that is relevant for the indirect detection of DM (through lepton preserving operators). This implies a perceived boost in the annihilation cross section in the Galaxy today relative to that derived for canonical thermal freeze-out, giving a natural explanation for the observed cosmic ray electron and positron excesses, without resorting to a Sommerfeld enhancement. These models motivate continued searches for DM with apparently nonthermal annihilation cross sections. The DM may also play a role in radiatively generating Majorana neutrino masses.

We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a full-field interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium.

We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called “extragalactic” diffuse $\gamma$-ray emission (EGB). This component of the diffuse $\gamma$-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modeling of the bright foreground diffuse Galactic $\gamma$-ray emission, the detected LAT sources, and the solar $\gamma$-ray emission. We find the spectrum of the EGB is consistent with a power law with a differential spectral index $\gamma =2.41\pm 0.05$ and intensity $I(>100\mathrm{MeV})=(1.03\pm 0.17)\times {10}^{-5}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$, where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.

We demonstrate the existence of a large number of exact solutions of plane Couette flow, which share the topology of known periodic solutions but are localized in one spatial dimension. Solutions of different size are organized in a snakes-and-ladders structure strikingly similar to that observed for simpler pattern-forming partial differential equations. These new solutions are a step towards extending the dynamical systems view of transitional turbulence to spatially extended flows.

We study the exact solution for two atomic particles in an optical lattice interacting via a Feshbach resonance. The analysis includes the influence of all higher bands, as well as the proper renormalization of molecular energy in the closed channel. This exact solution allows for the precise determination of the parameters in the Hubbard model and the two-particle bound state energy. We identify the regime, where a single band Hubbard model fails to describe the scattering properties of the atoms as well as the bound states energies.

The direct observation of a thermoelectric magnetohydrodynamic (TEMHD) flow has been achieved and is reported here. The origin of the flow is identified based on a series of qualitative tests and corresponds, quantitatively, with a swirling flow TEMHD model. A theory for determining the dominant driver of a free-surface flow, TEMHD or thermocapillary (TC), is found to be consistent with the experimental results. The use of the analytical form for an open geometry develops a new dimensionless parameter describing the ratio of TEMHD to TC generated flows.

Atomic vacancies have a strong impact in the mechanical, electronic, and magnetic properties of graphenelike materials. By artificially generating isolated vacancies on a graphite surface and measuring their local density of states on the atomic scale, we have shown how single vacancies modify the electronic properties of this graphenelike system. Our scanning tunneling microscopy experiments, complemented by tight-binding calculations, reveal the presence of a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be associated with the formation of local magnetic moments and implies a dramatic reduction of the charge carriers’ mobility. While vacancies in single layer graphene lead to magnetic couplings of arbitrary sign, our results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene just by randomly removing single C atoms.

Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. The most commonly used technique for this type of estimation is quantum filtering, using only past observations. We present the first experimental demonstration of quantum smoothing, a time-symmetric technique that uses past and future observations, for quantum parameter estimation. We consider both adaptive and nonadaptive quantum smoothing, and show that both are better than their filtered counterparts. For the problem of estimating a stochastically varying phase shift on a coherent beam, our theory predicts that adaptive quantum smoothing (the best scheme) gives an estimate with a mean-square error up to $2\sqrt{2}$ times smaller than nonadaptive filtering (the standard quantum limit). The experimentally measured improvement is $2.24\pm 0.14$.

The measurement of a quantitative and macroscopic parameter to estimate the global motility of a large population of swimming biological cells is a challenge. Experiments on the rheology of active suspensions have been performed. Effective viscosity of sheared suspensions of live unicellular motile microalgae (Chlamydomonas Reinhardtii) is far greater than for suspensions containing the same volume fraction of dead cells. In addition, suspensions show shear thinning behavior. We relate these macroscopic measurements to the orientation of individual swimming cells under flow and discuss our results in the light of several existing models.

The total entropy production of a trajectory can be split into an adiabatic and a nonadiabatic contribution, deriving, respectively, from the breaking of detailed balance via nonequilibrium boundary conditions or by external driving. We show that each of them, the total, the adiabatic, and the nonadiabatic trajectory entropy, separately satisfies a detailed fluctuation theorem.

We describe the measurement of the depth of maximum, $X_{\max }$, of the longitudinal development of air showers induced by cosmic rays. Almost 4000 events above ${10}^{18}\mathrm{eV}$ observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of $({106}_{-21}^{+35})\mathrm{g}/{\mathrm{cm}}^2/\mathrm{\text{decade}}$ below ${10}^{18.24\pm 0.05}\mathrm{eV}$, and $(24\pm 3)\mathrm{g}/{\mathrm{cm}}^2/\mathrm{\text{decade}}$ above this energy. The measured shower-to-shower fluctuations decrease from about 55 to $26\mathrm{g}/{\mathrm{cm}}^2$. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.