We show how the static magnetic field of a finite source can be transferred and routed to arbitrary long distances. This is achieved by using transformation optics, which results in a device made of a material with a highly anisotropic magnetic permeability. We show that a simplified version of the device, made by a superconducting-ferromagnet hybrid, also leads to an excellent transfer of the magnetic field. The latter is demonstrated with a proof-of-principle experiment where a ferromagnet tube coated with a superconductor improves the transfer of static magnetic fields with respect to conventional methods by a 400% factor over distances of 14 cm.

We report a first search for weakly interacting massive particles (WIMPs) using the background rejection capabilities of SuperCDMS. An exposure of 577 kg days was analyzed for WIMPs with mass $<30\mathrm{GeV}/c^2$, with the signal region blinded. Eleven events were observed after unblinding. We set an upper limit on the spin-independent WIMP-nucleon cross section of $1.2\times 10^{-42}{\mathrm{cm}}^2$ at $8\mathrm{GeV}/c^2$. This result is in tension with WIMP interpretations of recent experiments and probes new parameter space for WIMP-nucleon scattering for WIMP masses $<6\mathrm{GeV}/c^2$.

We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the $B$-mode power spectrum around $\ell \sim 80$. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of $\approx 300\mu {\mathrm{K}}_{\mathrm{CMB}}\sqrt{\mathrm{s}}$ . BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes $Q$ and $U$. In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of $B$-mode power over the base lensed-$\mathrm{\Lambda }\mathrm{CDM}$ expectation in the range $30<\ell <150$, inconsistent with the null hypothesis at a significance of $>5\sigma$. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power $\sim (5–10)\times$ smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with $3\sigma$ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at $1.7\sigma$. The observed $B$-mode power spectrum is well fit by a lensed-$\mathrm{\Lambda }\mathrm{CDM}+\text{tensor}$ theoretical model with tensor-to-scalar ratio $r=0.20_{-0.05}^{+0.07}$, with $r=0$ disfavored at $7.0\sigma$. Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets.

The simplest inflationary model $V=\frac{1}{2}{m}^2{\varphi }^2$ represents the benchmark for future constraints. For a quadratic potential, the quantity $(n_s-1)+r/4+11(n_s-1{)}^2/24$ vanishes (up to corrections which are cubic in slow roll) and can be used to parametrize small deviations from the minimal scenario. Future constraints on this quantity will be able to distinguish a quadratic potential from a pseudo-Nambu-Goldstone boson with $f\lesssim 30M_{\text{pl}}$ and set limits on the deviation from unity of the speed of sound $|c_s-1|\lesssim 3\times 10^{-2}$ (corresponding to an energy scale $\mathrm{\Lambda }\gtrsim 2\times 10^{16}\mathrm{GeV}$) and on the contribution of a second field to perturbations ($\lesssim 6\times 10^{-2}$). The limiting factor for these bounds will be the uncertainty on the spectral index. The error on the number of e-folds will be $\mathrm{\Delta }N\simeq 0.4$, corresponding to an error on the reheating temperature $\mathrm{\Delta }{T}_{\text{rh}}/T_{\text{rh}}\simeq 1.2$. We comment on the relevance of non-Gaussianity after BICEP2 results.

Osmosis across membranes is intrinsically associated with the concept of semipermeability. Here, however, we demonstrate that osmotic flow can be generated by solute gradients across nonselective, fully permeable nanochannels. Using a fluorescence imaging technique, we are able to measure the water flow rate inside single nanochannels to an unprecedented sensitivity of femtoliters per minute flow rates. Our results indicate the onset of a convective liquid motion under salinity gradients, from the higher to lower electrolyte concentration, which is attributed to diffusio-osmotic transport. To our knowledge, this is the first experimental evidence and quantitative investigation of this subtle interfacially driven transport, which need to be accounted for in nanoscale dynamics. Finally, diffusio-osmotic transport under a neutral polymer gradient is also demonstrated. The experiments highlight the entropic depletion of polymers that occurs at the nanochannel surface, resulting in convective flow in the opposite direction to that seen for electrolytes.

We report on temperature-dependent photocurrent measurements of high-quality dual-gated monolayer graphene $p\text{−}n$ junction devices. A photothermoelectric effect governs the photocurrent response in our devices, allowing us to track the hot-electron temperature and probe hot-electron cooling channels over a wide temperature range (4 to 300 K). At high temperatures ($T>T^{*}$), we found that both the peak photocurrent and the hot spot size decreased with temperature, while at low temperatures ($T<T^{*}$), we found the opposite, namely that the peak photocurrent and the hot spot size increased with temperature. This nonmonotonic temperature dependence can be understood as resulting from the competition between two hot-electron cooling pathways: (a) (intrinsic) momentum-conserving normal collisions that dominates at low temperatures and (b) (extrinsic) disorder-assisted supercollisions that dominates at high temperatures. Gate control in our high-quality samples allows us to resolve the two processes in the same device for the first time. The peak temperature $T^{*}$ depends on carrier density and disorder concentration, thus allowing for an unprecedented way of controlling graphene’s photoresponse.

Information on the size and shape of the neutron skin on ${}^{208}\mathrm{Pb}$ is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be $c_n=6.70\pm 0.03(\text{stat}\mathrm{.})\mathrm{fm}$ and $a_n=0.55\pm 0.01(\text{stat}{\mathrm{.})}_{-0.03}^{+0.02}(\text{sys}\mathrm{.})\mathrm{fm}$, respectively, corresponding to a neutron skin thickness $\mathrm{\Delta }{r}_{np}=0.15\pm 0.03(\text{stat}{\mathrm{.})}_{-0.03}^{+0.01}(\text{sys}\mathrm{.})\mathrm{fm}$. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of ${}^{208}\mathrm{Pb}$ has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

We use optical tweezers to study the effect of attractive versus repulsive DNA-DNA interactions on motor-driven viral packaging. Screening of repulsive interactions accelerates packaging, but induction of attractive interactions by ${\text{spermidine}}^{3+}$ causes heterogeneous dynamics. Acceleration is observed in a fraction of complexes, but most exhibit slowing and stalling, suggesting that attractive interactions promote nonequilibrium DNA conformations that impede the motor. Thus, repulsive interactions facilitate packaging despite increasing the energy of the theoretical optimum spooled DNA conformation.

Magnetization measurements and magnetotransmission spectroscopy of the solid oxygen $\alpha$ phase were performed in ultrahigh magnetic fields of up to 193 T. An abrupt increase in magnetization with large hysteresis was observed when pulsed magnetic fields greater than 120 T were applied. Moreover, the transmission of light significantly increased in the visible range. These experimental findings indicate that a first-order phase transition occurs in solid oxygen in ultrahigh magnetic fields, and that it is not just a magnetic transition. Considering the molecular rearrangement mechanism found in the ${\mathrm{O}}_2\text{−}{\mathrm{O}}_2$ dimer system, we conclude that the observed field-induced transition is caused by the antiferromagnetic phase collapsing and a change in the crystal structure.

High-resolution spectroscopy of the $2s_{1/2}-2p_{1/2}$ transition in the extreme ultraviolet region is shown to resolve the level splitting induced by the nuclear magnetic field of both the $2s_{1/2}$ and the $2p_{1/2}$ levels in lithiumlike ${{}^{141}\mathrm{Pr}}^{56+}$ and of the $2s_{1/2}2p_{1/2}$ ${}^3{P}_1$ level in berylliumlike ${{}^{141}\mathrm{Pr}}^{55+}$. The ${}^{141}\mathrm{Pr}$ ions are an ideal test of this measurement approach because their energy levels are known well from first principles and are unaffected by small energy contributions from QED and nuclear magnetization effects. The accuracy attained in the measured $196.5\pm 1.2\mathrm{meV}$ $2s_{1/2}$ splitting is more than an order of magnitude better than that achieved before using crystal spectroscopy of the $2s_{1/2}-2p_{3/2}$ x-ray transition and at the level needed to implement a proposed scheme for disentangling the contributions from QED and nuclear magnetization effects in higher-$Z$ ions, such as ${}^{209}\mathrm{Bi}$.

Small aerosols drift down a temperature or turbulence gradient since faster particles fly longer distances before equilibration. That fundamental phenomenon, called thermophoresis or turbophoresis, is widely encountered in nature and used in industry. It is universally believed that particles moving down the kinetic energy gradient must concentrate in minima (say, on walls in turbulence). Here, we show that this is incorrect: escaping minima is possible for inertial particles whose time of equilibration is longer than the time to reach the minimum. “The best way out is always through”: particles escape by flying through minima or reflecting from walls. We solve the problem analytically and find the phase transition as a sign change of the mean velocity. That means separation: light particles concentrate in a minimum while heavy particles spread away from it (gravity can reverse the effect). That discovery changes our understanding of that fundamental phenomenon and may find numerous applications.

The observation by Ke et al. [Science 338, 1177 (2012)] that large numbers of short, predesigned DNA strands can assemble into three-dimensional target structures came as a great surprise, as no colloidal self-assembling system has ever achieved the same degree of complexity. That failure seemed easy to rationalize: the larger the number of distinct building blocks, the higher the expected error rate for self-assembly. The experiments of Ke et al. have disproved this argument. Here, we report Monte Carlo simulations of the self-assembly of a DNA brick cube, comprising approximately 1000 types of DNA strand, using a simple model. We model the DNA strands as lattice tetrahedra with attractive patches, the interaction strengths of which are computed using a standard thermodynamic model. We find that, within a narrow temperature window, the target structure assembles with high probability. Our simulations suggest that misassembly is disfavored because of a slow nucleation step. As our model incorporates no aspect of DNA other than its binding properties, these simulations suggest that, with proper design of the building blocks, other systems, such as colloids, may also assemble into truly complex structures.

Room temperature electrically pumped inversionless polariton lasing is observed from a bulk GaN-based microcavity diode. The low nonlinear threshold for polariton lasing occurs at $169\mathrm{A}/{\mathrm{cm}}^2$ in the light-current characteristics, accompanied by a collapse of the emission linewidth and small blueshift of the emission peak. Measurement of angle-resolved luminescence, polariton condensation and occupation in momentum space, and output spatial coherence and polarization have also been made. A second threshold, due to conventional photon lasing, is observed at an injection of $44\mathrm{kA}/{\mathrm{cm}}^2$.

The first observation of the associated production of a single top quark and a $W$ boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of $12.2{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$ recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a $b$ quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant $t\overline{t}$ background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is $23.4\pm 5.4\text{pb}$, in agreement with the standard model prediction.

We report the first observation of single-top-quark production in the $s$ channel through the combination of the CDF and D0 measurements of the cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to $9.7{\mathrm{fb}}^{-1}$ per experiment. The measured cross section is ${\sigma }_s=1.29_{-0.24}^{+0.26}\mathrm{pb}$. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is $1.8\times {10}^{-10}$, corresponding to a significance of 6.3 standard deviations for the presence of an $s$-channel contribution to the production of single-top quarks.

We present the experimental observation of a large exchange coupling $J\approx 300\mu \mathrm{eV}$ between two ${}^{31}\mathrm{P}$ electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time $T_1\approx 4\mathrm{ms}$ at zero magnetic field agrees with the theoretical prediction for $J$-coupled ${}^{31}\mathrm{P}$ dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak $J$-coupling strengths.

Local measurements of the Hubble expansion rate are affected by structures like galaxy clusters or voids. Here we present a fully relativistic treatment of this effect, studying how clustering modifies the mean distance- (modulus-)redshift relation and its dispersion in a standard cold dark matter universe with a cosmological constant. The best estimates of the local expansion rate stem from supernova observations at small redshifts ($0.01<z<0.1$). It is interesting to compare these local measurements with global fits to data from cosmic microwave background anisotropies. In particular, we argue that cosmic variance (i.e., the effects of the local structure) is of the same order of magnitude as the current observational errors and must be taken into account in local measurements of the Hubble expansion rate.

The future redefinition of the international system of units in terms of natural constants requires a robust, high-precision quantum standard for the electrical base unit ampere. However, the reliability of any single-electron current source generating a nominally quantized output current $I=ef$ by delivering single electrons with charge $e$ at a frequency $f$ is eventually limited by the stochastic nature of the underlying quantum mechanical tunneling process. We experimentally explore a path to overcome this fundamental limitation by serially connecting clocked single-electron emitters with multiple in situ single-electron detectors. Correlation analysis of the detector signatures during current generation reveals erroneous pumping events and enables us to determine the deviation of the output current from the nominal quantized value $ef$. This demonstrates the concept of a self-referenced single-electron source for electrical quantum metrology.

The magnitude and variability of Earth’s biodiversity have puzzled scientists ever since paleontologic fossil databases became available. We identify and study a model of interdependent species where both endogenous and exogenous impacts determine the nonstationary extinction dynamics. The framework provides an explanation for the qualitative difference of marine and continental biodiversity growth. In particular, the stagnation of marine biodiversity may result from a global transition from an imbalanced to a balanced state of the species dependency network. The predictions of our framework are in agreement with paleontologic databases.

Resonant structures in $B^0\to {\psi }^{\prime }{\pi }^{-}{K}^{+}$ decays are analyzed by performing a four-dimensional fit of the decay amplitude, using $pp$ collision data corresponding to $3{\mathrm{fb}}^{-1}$ collected with the LHCb detector. The data cannot be described with $K^{+}{\pi }^{-}$ resonances alone, which is confirmed with a model-independent approach. A highly significant $Z(4430{)}^{-}\to {\psi }^{\prime }{\pi }^{-}$ component is required, thus confirming the existence of this state. The observed evolution of the $Z(4430{)}^{-}$ amplitude with the ${\psi }^{\prime }{\pi }^{-}$ mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be $1^{+}$.