We present a measurement of the ratio of the top-quark branching fractions $R=B(t\to Wb)/B(t\to Wq)$, where $q$ represents any quark flavor, in events with two charged leptons, imbalance in total transverse energy, and at least two jets. The measurement uses proton-antiproton collision data at center-of-mass energy 1.96 TeV, corresponding to an integrated luminosity of $8.7{\mathrm{fb}}^{-1}$ collected with the Collider Detector at Fermilab during Run II of the Tevatron. We measure $R$ to be $0.87\pm 0.07$, and extract the magnitude of the top-bottom quark coupling to be $|V_{tb}|=0.93\pm 0.04$, assuming three generations of quarks. Under these assumptions, a lower limit of $|V_{tb}|>0.85(0.87)$ at 95% (90%) credibility level is set.

We demonstrate a coexistence of coherent and incoherent modes in the optical comb generated by a passively mode-locked quantum dot laser. This is experimentally achieved by means of optical linewidth, radio frequency spectrum, and optical spectrum measurements and confirmed numerically by a delay-differential equation model showing excellent agreement with the experiment. We interpret the state as a chimera state.

Colloidal crystals belong to a new class of materials with unusual properties in which the big challenge is to grow large-scale structures of a given symmetry in a well-controlled and inexpensive way. Recently, template-assisted crystallization was successfully exploited experimentally in the case of colloidal particles dispersed in isotropic fluids. In liquid crystal (LC) colloids, particles are subjected to long-range anisotropic elastic forces originating from the anisotropic deformation of the underlying order parameter. These effective interactions are easily tunable by external electric or magnetic fields, light, temperature, or confinement and, thus, provide additional handles for better control of colloidal assembly. Here we use the coupling between microsculptured bounding surfaces and LC elasticity in order to guide the self-assembly of large-scale colloidal structures. We present explicit numerical calculations of the free energy landscape of colloidal particles in the presence of convex protrusions modeled as squared pyramids comparable to the size of the particles. We show the existence of strong trapping potentials that are able to efficiently localize the colloidal particles and withstand thermal fluctuations. Three-dimensional optical imaging experiments support the theoretical predictions.

Superfluid spin transport—dissipationless transport of spin—is theoretically studied in a ferromagnetic insulator with easy-plane anisotropy. We consider an open geometry where the spin current is injected into the ferromagnet from one side by a metallic reservoir with a nonequilibrium spin accumulation and ejected into another metallic reservoir located downstream. Spin transport is studied using a combination of magnetoelectric circuit theory, Landau-Lifshitz-Gilbert phenomenology, and microscopic linear-response theory. We discuss how spin superfluidity can be probed in a magnetically mediated negative electron-drag experiment.

The discovery of a standard-model-like Higgs boson and the hitherto absence of evidence for other new states may indicate that if weakly interacting massive particles (WIMPs) comprise cosmological dark matter, they are heavy compared to electroweak scale particles, $M\gg m_{W^{\pm }}$, $m_{Z^0}$. In this limit, the absolute cross section for a WIMP of given electroweak quantum numbers to scatter from a nucleon becomes computable in terms of standard model parameters. We develop effective field theory techniques to analyze the heavy WIMP limit of WIMP-nucleon scattering and present the first complete calculation of the leading spin-independent cross section in standard model extensions consisting of one or two electroweak $SU(2{)}_W\times U(1{)}_Y$ multiplets. The impact on scattering cross sections of the choice of WIMP quantum numbers and an extended Higgs sector is investigated.

We measure the total branching fraction of the flavor-changing neutral-current process $B\to X_s{\ell }^{+}{\ell }^{-}$, along with partial branching fractions in bins of dilepton and hadronic system ($X_s$) mass, using a sample of $471\times 10^6$ $\mathrm{\Upsilon }(4S)\to B\overline{B}$ events recorded with the BABAR detector. The admixture of charged and neutral $B$ mesons produced at PEP-II2 are reconstructed by combining a dilepton pair with 10 different $X_s$ final states. Extrapolating from a sum over these exclusive modes, we measure a lepton-flavor-averaged inclusive branching fraction $\mathcal{B}(B\to X_s{\ell }^{+}{\ell }^{-})=[6.73_{-0.64}^{+0.70}(\text{stat}{)}_{-0.25}^{+0.34}(\text{exp syst})\pm 0.50(\text{model syst})]\times 10^{-6}$ for $m_{{\ell }^{+}{\ell }^{-}}^2>0.1{\mathrm{GeV}}^2/c^4$. Restricting our analysis exclusively to final states from which a decaying $B$ meson’s flavor can be inferred, we additionally report measurements of the direct $CP$ asymmetry $A_{CP}$ in bins of dilepton mass; over the full dilepton mass range, we find $A_{CP}=0.04\pm 0.11\pm 0.01$ for a lepton-flavor-averaged sample.

We calculate the differential branching fractions and angular distributions of the rare decays $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$ and $B_s^0\to \varphi {\mu }^{+}{\mu }^{-}$, using for the first time form factors from unquenched lattice QCD. We focus on the kinematic region where the $K^{*}$ or $\varphi$ recoils softly; there, the newly available form factors are most precise and the nonlocal matrix elements can be included via an operator product expansion. Our results for the differential branching fractions calculated in the standard model are higher than the experimental data. We consider the possibility that the deviations are caused by new physics and perform a fit of the Wilson coefficients $C_9$ and $C_9^{\prime }$ to the experimental data for multiple $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$ and $B_s^0\to \varphi {\mu }^{+}{\mu }^{-}$ observables. In agreement with recent results from complementary studies, we obtain $C_9-C_9^{\mathrm{SM}}=-1.0\pm 0.6$ and $C_9^{\prime }=1.2\pm 1.0$, whose deviations from zero would indicate the presence of nonstandard fundamental interactions.

The time-dependent multiphoton ionization of xenon atoms is studied with femtosecond pulses in the excitation range of the $4d$ giant resonance at the photon energy of 93 eV. Benefiting from a new operation mode of the free electron laser FLASH, the measurements are performed with varying pulse durations. A strong dependence of the ion charge distribution on the pulse duration allows the different multiphoton mechanisms behind the multiple photoionization of xenon to be disentangled up to a charge state of ${\mathrm{Xe}}^{10+}$. The results up to ${\mathrm{Xe}}^{8+}$ are well explained by sequences of single photon, multiphoton, and Auger processes, but higher charge state generation suggests the need for collective electron multiphoton excitations.

The coherent light-matter interaction at the single-photon and electronic qubit level promises to be a remarkable potential for nonclassical information processing. Besides the efforts of improving the figure of merit of the cavities, here we demonstrate strong anharmonicity in the polariton dressed states via dark state resonances in a highly dissipative cavity. It is shown that the vacuum Rabi oscillation occurs for a single quantum emitter inside a cavity even with the bosonic decay-to-interaction rate ratio exceeding ${10}^2$, when the photon field is coupled to an auxiliary high-$Q$ cavity. Moreover, photon blockade is observable in such a highly dissipative cavity quantum electrodynamics system. This study provides a promising platform for overcoming decoherence and advancing the coherent manipulation of polariton qubits.

We consider two mean-field models of structural glasses, the random energy model and the $p$-spin model (PSM), and we show that the finite-size fluctuations of the freezing temperature are described by extreme-value statistics (EVS) distributions, establishing an unprecedented connection between EVS and the freezing transition of structural glasses. For the random energy model, the freezing-temperature fluctuations are described by the Gumbel EVS distribution, while for the PSM the freezing temperature fluctuates according to the Tracy-Widom EVS distribution, which has been recently discovered within the theory of random matrices. For the PSM, we provide an analytical argument showing that the emergence of the Tracy-Widom distribution can be understood in terms of the statistics of glassy metastable states.

Topological superconductors (TSCs), featuring fully gapped bulk and gapless surface states as well as Majorana fermions, have potential applications in fault-tolerant topological quantum computing. Because TSCs are very rare in nature, an alternative way to study the TSC is to artificially introduce superconductivity into the surface states of a topological insulator through the proximity effect [X. L. Qi, T. L. Hughse, S. Raghu, and S. C. Zhang, Phys. Rev. Lett. 102, 187001 (2009); L. Fu and C. L. Kane, Phys. Rev. Lett. 100, 096407 (2008); J. Alicea, Rep. Prog. Phys. 75, 076501 (2012); C. W. J. Beenakker, Annu. Rev. Condens. Matter Phys. 4, 113 (2013)]. Here we report the experimental realization of the proximity effect–induced TSC in ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ thin films grown on a ${\mathrm{NbSe}}_2$ substrate, as demonstrated by the density of states probed using scanning tunneling spectroscopy. We observed Abrikosov vortices and Andreev lower energy bound states on the surface of the topological insulator, with the superconducting coherence length depending on the film thickness and the magnetic field. These results also indicate that the topological surface states of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ thin films are superconducting and, thus, that the ${\mathrm{Bi}}_2{\mathrm{Te}}_3/{\mathrm{NbSe}}_2$ is an artificial TSC. The feasibility of fabricating a TSC with an individual Majorana fermion bound to a superconducting vortex for topological quantum computing is discussed.

We report the kinetics of twin-boundary motion in the ferromagnetic shape-memory alloy of Ni-Mn-Ga as measured by in situ high energy synchrotron diffraction. The temporal evolution of twin reorientation during the application of a magnetic field is described by thermally activated creep motion of twin boundaries over a distribution of energy barriers. The dynamical creep exponent $\mu$ was found to be $\sim 0.5$, suggesting that the distribution of energy barriers is a result of short-range disorders.

We study a particular mechanism of cell motility allowing a precise formulation of the condition of optimal trade-off between performance and metabolic cost. In the model, a steadily crawling fragment is represented by a layer of active gel placed on a frictional surface and driven by contraction only. We find analytically the distribution of contractile elements (pullers) ensuring that the efficiency of self-propulsion is maximal. We then show that natural assumptions about advection and diffusion of pullers produce a distribution that is remarkably close to the optimal one and is qualitatively similar to the one observed in experiments on fish keratocytes.

The degree of non-Markovianity of quantum processes has been characterized in several different ways in the recent literature. However, the relationship between the non-Markovian behavior and the flow of information between the system and the environment through an entropic measure has not been yet established. We propose an entanglement-based measure of non-Markovianity by employing the concept of assisted knowledge, where the environment $\mathcal{E}$, acquires information about a system $\mathcal{S}$, by means of its measurement apparatus $\mathcal{A}$. The assisted knowledge, based on the accessible information in terms of von Neumann entropy, monotonically increases in time for all Markovian quantum processes. We demonstrate that the signatures of non-Markovianity can be captured by the nonmonotonic behavior of the assisted knowledge. We explore this scenario for a two-level system undergoing a relaxation process, through an experimental implementation using an optical approach that allows full access to the state of the environment.

Motivated by the recent theoretical and experimental progress in implementing topological orders with photons, we analyze photonic systems with different topologies and present a scheme to probe their topological features. Specifically, we propose a scheme to modify the boundary phases to manipulate edge state dynamics. Such a scheme allows one to measure the winding number of the edge states. Furthermore, we discuss the effect of loss and disorder on the validity of our approach.