Bicritical points, at which two distinct symmetry-broken phases become simultaneously unstable, are typical for spin-flop metamagnetism. Interestingly, the heavy-fermion compound YbAgGe also possesses such a bicritical point (BCP) with a low temperature $T_{\mathrm{BCP}}\approx 0.3\mathrm{K}$ at a magnetic field of ${\mu }_0{H}_{\mathrm{BCP}}\approx 4.5\mathrm{T}$. In its vicinity, YbAgGe exhibits anomalous behavior that we attribute to the influence of a quantum bicritical point that is close in parameter space yet can be reached by tuning $T_{\mathrm{BCP}}$ further to zero. Using high-resolution measurements of the magnetocaloric effect, we demonstrate that the magnetic Grüneisen parameter ${\Gamma }_H$ indeed both changes sign and diverges as required for quantum criticality. Moreover, ${\Gamma }_H$ displays a characteristic scaling behavior but only on the low-field side $H\lesssim H_{\mathrm{BCP}}$, indicating a pronounced asymmetry with respect to the critical field. We speculate that the small value of $T_{\mathrm{BCP}}$ is related to the geometric frustration of the Kondo lattice of YbAgGe.

We propose a setup to realize time-reversal-invariant topological superconductors in quantum wires, proximity coupled to conventional superconductors. We consider a model of quantum wire with strong spin-orbit coupling and proximity coupling to two $s$-wave superconductors. When the relative phase between the two superconductors is $\varphi =\pi$ a Kramers pair of Majorana zero modes appears at each edge of the wire. We study the robustness of the phase in the presence of both time-reversal-invariant and time-reversal-breaking perturbations. In addition, we show that the system forms a natural realization of a fermion parity pump, switching the local fermion parity of both edges when the relative phase between the superconductors is changed adiabatically by $2\pi$.

We investigate numerically the collisions of two distinguishable quantum matter-wave bright solitons in a one-dimensional harmonic trap. We show that such collisions can be used to generate mesoscopic Bell states that can reliably be distinguished from statistical mixtures. Calculation of the relevant $s$-wave scattering lengths predicts that such states could potentially be realized in quantum-degenerate mixtures of ${}^{85}\mathrm{Rb}$ and ${}^{133}\mathrm{Cs}$. In addition to fully quantum simulations for two distinguishable two-particle solitons, we use a mean-field description supplemented by a stochastic treatment of quantum fluctuations in the soliton’s center of mass: we demonstrate the validity of this approach by comparison to a mathematically rigorous effective potential treatment of the quantum many-particle problem.

We introduce and characterize two different measures which quantify the level of synchronization of coupled continuous variable quantum systems. The two measures allow us to extend to the quantum domain the notions of complete and phase synchronization. The Heisenberg principle sets a universal bound to complete synchronization. The measure of phase synchronization is, in principle, unbounded; however, in the absence of quantum resources (e.g., squeezing) the synchronization level is bounded below a certain threshold. We elucidate some interesting connections between entanglement and synchronization and, finally, discuss an application based on quantum optomechanical systems.

Two-dimensional simulations, both Vlasov and particle-in-cell, are presented that show the evolution of the field and electron distribution of finite-width, nonlinear electron plasma waves. The intrinsically intertwined effects of self-focusing and dissipation of field energy caused by electron trapping are studied in simulated systems that are hundreds of wavelengths long in the transverse direction but only one wavelength long and periodic in the propagation direction. From various initial wave states, both the width at focus ${\Delta }_m$ relative to the initial width ${\Delta }_0$ and the maximum field amplitude at focus are shown to be a function of the growth rate of the transverse modulational instability ${\gamma }_{\mathrm{TPMI}}$ divided by the loss rate of field energy ${\nu }_E$ to electrons escaping the trapping region. With dissipation included, an amplitude threshold for self-focusing ${\gamma }_{\mathrm{TPMI}}/{\nu }_E\sim 1$ is found that supports the analysis of Rose [Phys. Plasmas 12, 012318 (2005)].

Development of experimental techniques for characterization of magnetic properties at high spatial resolution is essential for progress in miniaturization of magnetic devices, for example, in data storage media. Inelastic scattering of electron vortex beams (EVBs) was recently reported to contain atom-specific magnetic information. We develop a theoretical description of inelastic scattering of EVBs on crystals and perform simulations for EVBs of different diameters. We show that use of an EVB wider than an interatomic distance does not provide any advantage over an ordinary convergent beam without angular momentum. On the other hand, in the atomic-resolution limit, electron energy loss spectra measured by EVBs are strongly sensitive to the spin and orbital magnetic moments of studied matter, when channeling through or very close to the atomic columns. Our results demonstrate the boundaries for efficient use of EVBs in measurement of magnetic properties.

Strong damping enhancement in nm-thick yttrium iron garnet (YIG) films due to Pt capping layers was observed. This damping is substantially larger than the expected damping due to conventional spin pumping, is accompanied by a shift in the ferromagnetic resonance field, and can be suppressed by the use of a Cu spacer in between the YIG and Pt films. The data indicate that such damping may originate from the ferromagnetic ordering in Pt atomic layers near the $\mathrm{YIG}/\mathrm{Pt}$ interface and the dynamic exchange coupling between the ordered Pt spins and the spins in the YIG film.

Electrically induced reorientation of nematic liquid crystal (NLC) molecules caused by dielectric anisotropy of the material is a fundamental phenomenon widely used in modern technologies. Its Achilles heel is a slow (millisecond) relaxation from the field-on to the field-off state. We present an electro-optic effect in an NLC with a response time of about 30 ns to both the field-on and field-off switching. This effect is caused by the electric field induced modification of the order parameters and does not require reorientation of the optic axis (director).

Quantum systems in mixed states can be unentangled and yet still nonclassically correlated. These correlations can be quantified by the quantum discord and might provide a resource for quantum information processing tasks. By precisely controlling the interaction of two ionic qubits with their environment, we investigate the capability of noise to generate discord. Firstly, we show that noise acting on only one quantum system can generate discord between two. States generated in this way are restricted in terms of the rank of their correlation matrix. Secondly, we show that classically correlated noise processes are capable of generating a much broader range of discordant states with correlation matrices of any rank. Our results show that noise processes prevalent in many physical systems can automatically generate nonclassical correlations and highlight fundamental differences between discord and entanglement.

We demonstrate precise control of the coupling of each of two trapped ions to the mode of an optical resonator. When both ions are coupled with near-maximum strength, we generate ion-ion entanglement heralded by the detection of two orthogonally polarized cavity photons. The entanglement fidelity with respect to the Bell state ${\Psi }^{+}$ reaches $F\ge (91.9\pm 2.5)\%$. This result represents an important step toward distributed quantum computing with cavities linking remote atom-based registers.

We control quantum fluctuations to create the ground state magnetic phases of a classical Ising model with a tunable longitudinal magnetic field using a system of 6 to 10 atomic ion spins. Because of the long-range Ising interactions, the various ground state spin configurations are separated by multiple first-order phase transitions, which in our zero temperature system cannot be driven by thermal fluctuations. We instead use a transverse magnetic field as a quantum catalyst to observe the first steps of the complete fractal devil’s staircase, which emerges in the thermodynamic limit and can be mapped to a large number of many-body and energy-optimization problems.

We show that the recently found anti–de Sitter (AdS)-plane and AdS-spherical wave solutions of quadratic curvature gravity also solve the most general higher derivative theory in $D$ dimensions. More generally, we show that the field equations of such theories reduce to an equation linear in the Ricci tensor for Kerr-Schild spacetimes having type-$N$ Weyl and type-$N$ traceless Ricci tensors.

This Letter describes new work on the determination of the Newtonian constant of gravitation, $G$, carried out at the BIPM since publication of the first results in 2001. The apparatus has been completely rebuilt and extensive tests carried out on the key parameters needed to produce a new value for $G$. The basic principles of the experiment remain the same, namely a torsion balance suspended from a wide, thin Cu-Be strip with two modes of operation, free deflection (Cavendish) and electrostatic servo control. The result from the new work is: $G=6.67545(18)\times {10}^{-11}{\mathrm{m}}^3{\mathrm{kg}}^{-1}{\mathrm{s}}^{-2}$ with a standard uncertainty of 27 ppm. This is 21 ppm below our 2001 result but 241 ppm above The CODATA 2010 value, which has an assigned uncertainty of 120 ppm. This confirms the discrepancy of our results with the CODATA value and highlights the wide divergence that now exists in recent values of $G$. The many changes made to the apparatus lead to the formal correlation between our two results being close to zero. Being statistically independent and statistically consistent, the two results taken together provide a unique contribution to determinations of $G$.

The proton is arguably the most fundamental of nature’s readily detectable building blocks. It is at the heart of every nucleus and has never been observed to decay. It is nevertheless a composite object, defined by its valence-quark content: $u+u+d$—i.e., two up ($u$) quarks and one down ($d$) quark; and the manner by which they influence, inter alia, the distribution of charge and magnetization within this bound state. Much of novelty has recently been learned about these distributions; and it now appears possible that the proton’s momentum-space charge distribution possesses a zero. Experiments in the coming decade should answer critical questions posed by this and related advances; we explain how such new information may assist in charting the origin and impact of key emergent phenomena within the strong interaction. Specifically, we show that the possible existence and location of a zero in the proton’s electric form factor are a measure of nonperturbative features of the quark-quark interaction in the standard model, with particular sensitivity to the running of the dressed-quark mass.

Results are presented from a search for the rare decays $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ in $pp$ collisions at $\sqrt{s}=7$ and 8 TeV, with data samples corresponding to integrated luminosities of 5 and $20{\mathrm{fb}}^{-1}$, respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})=({3.0}_{-0.9}^{+1.0})\times {10}^{-9}$, where the uncertainty includes both statistical and systematic contributions. An excess of $B_s^0\to {\mu }^{+}{\mu }^{-}$ events with respect to background is observed with a significance of 4.3 standard deviations. For the decay $B^0\to {\mu }^{+}{\mu }^{-}$ an upper limit of $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<1.1\times {10}^{-9}$ at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.

A search for the rare decays $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ is performed at the LHCb experiment. The data analyzed correspond to an integrated luminosity of $1{\mathrm{fb}}^{-1}$ of $pp$ collisions at a center-of-mass energy of 7 TeV and $2{\mathrm{fb}}^{-1}$ at 8 TeV. An excess of $B_s^0\to {\mu }^{+}{\mu }^{-}$ signal candidates with respect to the background expectation is seen with a significance of 4.0 standard deviations. A time-integrated branching fraction of $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})=({2.9}_{-1.0}^{+1.1})\times {10}^{-9}$ is obtained and an upper limit of $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<7.4\times {10}^{-10}$ at 95% confidence level is set. These results are consistent with the standard model expectations.

The ratio of the ${\Lambda }_b^0$ baryon lifetime to that of the ${\overline{B}}^0$ meson is measured using $1.0{\mathrm{fb}}^{-1}$ of integrated luminosity in 7 TeV center-of-mass energy $pp$ collisions at the LHC. The ${\Lambda }_b^0$ baryon is observed for the first time in the decay mode ${\Lambda }_b^0\to J/\psi p{K}^{-}$, while the ${\overline{B}}^0$ meson decay used is the well known ${\overline{B}}^0\to J/\psi {\pi }^{+}{K}^{-}$ mode, where the ${\pi }^{+}{K}^{-}$ mass is consistent with that of the ${\overline{K}}^{*0}(892)$ meson. The ratio of lifetimes is measured to be $0.976\pm 0.012\pm 0.006$, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the ${\overline{B}}^0$ meson lifetime, the ${\Lambda }_b^0$ lifetime is found to be $1.482\pm 0.018\pm 0.012\mathrm{ps}$. In both cases, the first uncertainty is statistical and the second systematic.

Azimuthally anisotropic distributions of $D^0$, $D^{+}$, and $D^{*+}$ mesons were studied in the central rapidity region ($|y|<0.8$) in Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient $v_2$ (commonly denoted elliptic flow) was measured in the centrality class 30%–50% as a function of the $D$ meson transverse momentum $p_T$, in the range $2–16\mathrm{GeV}/c$. The measured $v_2$ of $D$ mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range $2<p_T<6\mathrm{GeV}/c$ with $5.7\sigma$ significance, based on the combination of statistical and systematic uncertainties.

Photoabsorption by and fluorescence of the $K\alpha$ transitions in highly charged iron ions are essential mechanisms for x-ray radiation transfer in astrophysical environments. We study photoabsorption due to the main $K\alpha$ transitions in highly charged iron ions from heliumlike to fluorinelike (${\mathrm{Fe}}^{24+}$ to ${\mathrm{Fe}}^{17+}$) using monochromatic x rays around 6.6 keV at the PETRA III synchrotron photon source. Natural linewidths were determined with hitherto unattained accuracy. The observed transitions are of particular interest for the understanding of photoexcited plasmas found in x-ray binary stars and active galactic nuclei.

We investigate experimentally the validity of proposed theories extending the tunneling approximation towards the multiphoton regime in strong-field ionization of helium. We employ elliptically polarized laser pulses and demonstrate how the influence of the ion potential on the released electron encoded in the measured observable provides the desired sensitivity to detect nonadiabatic effects in tunnel ionization. Our results show that for a large intensity range the proposed nonadiabatic theories contradict the experimental trends of the data, while adiabatic assumptions are confirmed.