The data sample of ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ decays acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$, is inspected for the presence of $J/\psi p$ or $J/\psi K^{-}$ contributions with minimal assumptions about $K^{-}p$ contributions. It is demonstrated at more than nine standard deviations that ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ decays cannot be described with $K^{-}p$ contributions alone, and that $J/\psi p$ contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for $P_c^{+}\to J/\psi p$ charmonium-pentaquark states in the same data sample.

A full amplitude analysis of ${\mathrm{\Lambda }}_b^0\to J/\psi p{\pi }^{-}$ decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV $pp$ collisions, corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$. A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations $N\to p{\pi }^{-}$, either the $P_c(4380{)}^{+}$ and $P_c(4450{)}^{+}\to J/\psi p$ states, previously observed in ${\mathrm{\Lambda }}_b^0\to J/\psi p{K}^{-}$ decays, or the $Z_c(4200{)}^{-}\to J/\psi {\pi }^{-}$ state, previously reported in $B^0\to J/\psi K^{+}{\pi }^{-}$ decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the $P_c(4380{)}^{+}$ and $P_c(4450{)}^{+}$ production rates expected from their previous observation taking account of Cabibbo suppression.

We present an improved search for neutrinoless double-beta ($0\nu \beta \beta$) decay of ${}^{136}\mathrm{Xe}$ in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ${}^{110m}\mathrm{Ag}$ contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the $0\nu \beta \beta$ decay half-life of $T_{1/2}^{0\nu }>1.07\times 10^{26}\mathrm{yr}$ at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61–165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.

Understanding the mechanism of fracture is essential for material and process design. While the initiation of fracture in brittle solids is generally associated with the preexistence of material imperfections, the mechanism for initiation of fracture in viscoelastic fluids, e.g., polymer melts and solutions, remains an open question. We use high speed imaging to visualize crack propagation in entangled polymer liquid filaments under tension. The images reveal the simultaneous propagation of multiple cracks. The critical stress and strain for the onset of crack propagation are found to be highly reproducible functions of the stretch rate, while the position of initiation is completely random. The reproducibility of conditions for fracture points to a mechanism for crack initiation that depends on the dynamic state of the material alone, while the crack profiles reveal the mechanism of energy dissipation during crack propagation.

We prepare number stabilized ultracold atom clouds through the real-time analysis of nondestructive images and the application of feedback. In our experiments, the atom number $N\sim 10^6$ is determined by high precision Faraday imaging with uncertainty $\mathrm{\Delta }N$ below the shot noise level, i.e., $\mathrm{\Delta }N<\sqrt{N}$. Based on this measurement, feedback is applied to reduce the atom number to a user-defined target, whereupon a second imaging series probes the number stabilized cloud. By this method, we show that the atom number in ultracold clouds can be prepared below the shot noise level.

A Corbino ring geometry is utilized to analyze edge and bulk conductance of $\mathrm{InAs}/\mathrm{GaSb}$ quantum well structures. We show that edge conductance exists in the trivial regime of this theoretically predicted topological system with a temperature-insensitive linear resistivity per unit length in the range of $2\mathrm{k}\mathrm{\Omega }/\mu \mathrm{m}$. A resistor network model of the device is developed to decouple the edge conductance from the bulk conductance, providing a quantitative technique to further investigate the nature of this trivial edge conductance, conclusively identified here as being of $n$ type.

Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$) layer in a $\mathrm{Py}/\mathrm{Cu}/{\mathrm{Cu}}_{75}{\mathrm{Mn}}_{25}/\mathrm{Cu}/\mathrm{Co}$ multilayer to pump a pure ac spin current into the ${\mathrm{Cu}}_{75}{\mathrm{Mn}}_{25}$ and Co layers, and then directly probe the spin current within the ${\mathrm{Cu}}_{75}{\mathrm{Mn}}_{25}$ layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the ${\mathrm{Cu}}_{75}{\mathrm{Mn}}_{25}$ layer.

We theoretically give an infinite number of metastable crystal structures for the superconducting sulfur hydride ${\mathrm{H}}_x\mathrm{S}$ under pressure. Previously predicted crystalline phases of ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{H}}_3\mathrm{S}$ have been thought to have important roles for experimentally observed low and high $T_c$, respectively. The newly found structures are long-period modulated crystals where slablike ${\mathrm{H}}_2\mathrm{S}$ and ${\mathrm{H}}_3\mathrm{S}$ regions intergrow on a microscopic scale. The extremely small formation enthalpy for the ${\mathrm{H}}_2\mathrm{S}\text{−}{\mathrm{H}}_3\mathrm{S}$ boundary indicated by first-principles calculations suggests possible alloying of these phases through the formation of local ${\mathrm{H}}_3\mathrm{S}$ regions. The modulated structures and gradual alloying transformations between them not only explain the peculiar pressure dependence of $T_c$ in sulfur hydride observed experimentally, but also could prevail in the experimental samples under various compression schemes.

We investigate experimentally the quenching of a liquid pancake, obtained through the impact of a water drop on a cold solid substrate ($0°\mathrm{C}$ to $-60°\mathrm{C}$). We show that, below a certain substrate temperature, fractures appear on the frozen pancake and the crack patterns change from a 2D fragmentation regime to a hierarchical fracture regime as the thermal shock increases. The different regimes are discussed and the transition temperatures are estimated through classical fracture scaling arguments. Finally, a phase diagram presents how these regimes can be controlled by the drop impact parameters.

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous ${\nu }_{\mu }$ or ${\overline{\nu }}_{\mu }$ disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the $3+1$ model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to ${\sin }^{2}2{\theta }_{24}\le 0.02$ at $\mathrm{\Delta }{m}^2\sim 0.3{\mathrm{eV}}^2$ at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of $|U_{e4}{|}^2$.

We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.

It may soon be possible for Advanced LIGO to detect hundreds of binary black hole mergers per year. We show how the accumulation of many such measurements will allow for the detection of gravitational-wave memory: a permanent displacement of spacetime that comes from strong-field, general relativistic effects. We estimate that Advanced LIGO operating at design sensitivity may be able to make a signal-to-noise ratio 3 (5) detection of memory with $\sim 35(90)$ events with masses and distance similar to GW150914. We highlight the importance of incorporating higher-order gravitational-wave modes for parameter estimation of binary black hole mergers, and describe how our methods can also be used to detect higher-order modes themselves before Advanced LIGO reaches design sensitivity.

The $CP$ asymmetry in the mixing of $B_s^0$ and ${\overline{B}}_s^0$ mesons is measured in proton-proton collision data corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$, recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV. Semileptonic $B_s^0$ and ${\overline{B}}_s^0$ decays are studied in the inclusive mode $D_s^{\mp }{\mu }^{\pm }{\stackrel{(-)}{\nu }}_{\mu }X$ with the $D_s^{\mp }$ mesons reconstructed in the $K^{+}{K}^{-}{\pi }^{\mp }$ final state. Correcting the observed charge asymmetry for detection and background effects, the $CP$ asymmetry is found to be $a_{\text{sl}}^s=(0.39\pm 0.26\pm 0.20)\%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\text{sl}}^s$ to date. It is consistent with the prediction from the standard model and will constrain new models of particle physics.

Following an idea by Joyner et al. [Europhys. Lett. 107, 50004 (2014)], a microwave graph with an antiunitary symmetry $T$ obeying $T^2=-1$ is realized. The Kramers doublets expected for such systems are clearly identified and can be lifted by a perturbation which breaks the antiunitary symmetry. The observed spectral level spacings distribution of the Kramers doublets is in agreement with the predictions from the Gaussian symplectic ensemble expected for chaotic systems with such a symmetry.

Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous ${\mathrm{Ag}}_4{\mathrm{In}}_3{\mathrm{Sb}}_{67}{\mathrm{Te}}_{26}$. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

Topological numbers can characterize the transition between different topological phases, which are not described by Landau’s paradigm of symmetry breaking. Since the discovery of the quantum Hall effect, more topological phases have been theoretically predicted and experimentally verified. However, it is still an experimental challenge to directly measure the topological numbers of various predicted topological phases. In this Letter, we demonstrate quantum simulation of topological phase transition of a quantum wire (QW), by precisely modulating the Hamiltonian of a single nitrogen-vacancy (NV) center in diamond. Deploying a quantum algorithm of finding eigenvalues, we reliably extract both the dispersion relations and topological numbers. This method can be further generalized to simulate more complicated topological systems.

We demonstrate laser-driven two-qubit and single-qubit logic gates with respective fidelities 99.9(1)% and 99.9934(3)%, significantly above the $\approx 99\%$ minimum threshold level required for fault-tolerant quantum computation, using qubits stored in hyperfine ground states of calcium-43 ions held in a room-temperature trap. We study the speed-fidelity trade-off for the two-qubit gate, for gate times between $3.8\mu \mathrm{s}$ and $520\mu \mathrm{s}$, and develop a theoretical error model which is consistent with the data and which allows us to identify the principal technical sources of infidelity.

We report high-fidelity laser-beam-induced quantum logic gates on magnetic-field-insensitive qubits comprised of hyperfine states in ${{}^9\mathrm{Be}}^{+}$ ions with a memory coherence time of more than 1 s. We demonstrate single-qubit gates with an error per gate of $3.8(1)\times {10}^{-5}$. By creating a Bell state with a deterministic two-qubit gate, we deduce a gate error of $8(4)\times {10}^{-4}$. We characterize the errors in our implementation and discuss methods to further reduce imperfections towards values that are compatible with fault-tolerant processing at realistic overhead.

In Coulomb drag, a current flowing in one conductor can induce a voltage across an adjacent conductor via the Coulomb interaction. The mechanisms yielding drag effects are not always understood, even though drag effects are sufficiently general to be seen in many low-dimensional systems. In this Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot and, through both experimental and theoretical arguments, identify cotunneling as essential to obtaining a correct qualitative understanding of the drag behavior.

We point out that the gravitational-wave event GW150914 observed by the LIGO detectors can be explained by the coalescence of primordial black holes (PBHs). It is found that the expected PBH merger rate would exceed the rate estimated by the LIGO Scientific Collaboration and the Virgo Collaboration if PBHs were the dominant component of dark matter, while it can be made compatible if PBHs constitute a fraction of dark matter. Intriguingly, the abundance of PBHs required to explain the suggested lower bound on the event rate, $>2\mathrm{events}{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, roughly coincides with the existing upper limit set by the nondetection of the cosmic microwave background spectral distortion. This implies that the proposed PBH scenario may be tested in the not-too-distant future.