The dark photon $A^{\prime }$ and the dark Higgs boson $h^{\prime }$ are hypothetical constituents featured in a number of recently proposed dark sector models. Assuming prompt decays of both dark particles, we search for their production in the so-called Higgstrahlung channel $e^{+}{e}^{-}\to A^{\prime }{h}^{\prime }$, with $h^{\prime }\to A^{\prime }{A}^{\prime }$. We investigate ten exclusive final states with $A^{\prime }\to e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, or ${\pi }^{+}{\pi }^{-}$ in the mass ranges $0.1\mathrm{GeV}/c^2<m_{A^{\prime }}<3.5\mathrm{GeV}/c^2$ and $0.2\mathrm{GeV}/c^2<m_{h^{\prime }}<10.5\mathrm{GeV}/c^2$. We also investigate three inclusive final states $2(e^{+}{e}^{-})X$, $2({\mu }^{+}{\mu }^{-})X$, and $(e^{+}{e}^{-})({\mu }^{+}{\mu }^{-})X$, where $X$ denotes a dark photon candidate detected via missing mass, in the mass ranges $1.1\mathrm{GeV}/c^2<m_{A^{\prime }}<3.5\mathrm{GeV}/c^2$ and $2.2\mathrm{GeV}/c^2<m_{h^{\prime }}<10.5\mathrm{GeV}/c^2$. Using the entire $977{\mathrm{fb}}^{-1}$ data set collected by Belle, we observe no significant signal. We obtain individual and combined 90% credibility level upper limits on the branching fraction times the Born cross section, $\mathcal{B}\times {\sigma }_{\text{Born}}$, on the Born cross section ${\sigma }_{\text{Born}}$, and on the dark photon coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, ${\alpha }_D\times {\epsilon }^2$. These limits improve upon and cover wider mass ranges than previous experiments. The limits from the final states $3({\pi }^{+}{\pi }^{-})$ and $2(e^{+}{e}^{-})X$ are the first placed by any experiment. For ${\alpha }_D$ equal to $1/137$, $m_{h^{\prime }}<8\mathrm{GeV}/c^2$, and $m_{A^{\prime }}<1\mathrm{GeV}/c^2$, we exclude values of the mixing parameter $\epsilon$ above $\sim 8\times {10}^{-4}$.

Results on the production of the double strange cascade hyperon ${\mathrm{\Xi }}^{-}$ are reported for collisions of $p(3.5\mathrm{GeV})+\mathrm{Nb}$, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time, subthreshold ${\mathrm{\Xi }}^{-}$ production is observed in proton-nucleus interactions. Assuming a ${\mathrm{\Xi }}^{-}$ phase-space distribution similar to that of $\mathrm{\Lambda }$ hyperons, the production probability amounts to $P_{{\mathrm{\Xi }}^{-}}=[2.0\pm 0.4(\text{stat})\pm 0.3(\text{norm})\pm 0.6(\text{syst})]\times 10^{-4}$ resulting in a ${\mathrm{\Xi }}^{-}/(\mathrm{\Lambda }+{\mathrm{\Sigma }}^0)$ ratio of $P_{{\mathrm{\Xi }}^{-}}/P_{\mathrm{\Lambda }+{\mathrm{\Sigma }}^0}=[1.2\pm 0.3(\text{stat})\pm 0.4(\text{syst})]\times 10^{-2}$. Available model predictions are significantly lower than the measured ${\mathrm{\Xi }}^{-}$ yield.

We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with ${{\mathrm{C}}_2}^{-}$, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped ${{\mathrm{C}}_2}^{-}$, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.

Cavitation bubbles induce impulsive forces on surrounding substrates, particles, or surfaces. Even though cavitation is a traditional topic in fluid mechanics, current understanding and studies do not capture the effect of cavitation on suspended objects in fluids. In the present work, the dynamics of a spherical particle due to a cavitation bubble is experimentally characterized and compared with an analytical model. Three phases are observed: the growth of the bubble where the particle is pushed away, its collapse where the particle approaches the bubble, and a longer time scale postcollapse where the particle continues to move toward the collapsed bubble. The particle motion in the longer time scale presumably results from the asymmetric cavitation evolution at an earlier time. Our theory considering the asymmetric bubble dynamics shows that the particle velocity strongly depends on the distance from the bubble as an inverse-fourth-power law, which is in good agreement with our experimentation. This study sheds light on how small free particles respond to cavitation bubbles in fluids.

X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{Mn}}_2{\mathrm{As}}_2$ show that the ferromagnetism below $T_{\mathrm{C}}\approx 100\mathrm{K}$ arises in the As $4p$ conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below $T_{\mathrm{C}}$, however, a clear XMCD signal is found at the As $K$ edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic $\mathbf{c}$ axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As $4p$ conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.

We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

We study the infinite-temperature properties of an infinite sequence of random quantum spin chains using a real-space renormalization group approach, and demonstrate that they exhibit nonergodic behavior at strong disorder. The analysis is conveniently implemented in terms of $\mathrm{SU}(2{)}_k$ anyon chains that include the Ising and Potts chains as notable examples. Highly excited eigenstates of these systems exhibit properties usually associated with quantum critical ground states, leading us to dub them “quantum critical glasses.” We argue that random-bond Heisenberg chains self-thermalize and that the excited-state entanglement crosses over from volume-law to logarithmic scaling at a length scale that diverges in the Heisenberg limit $k\to \infty$. The excited state fixed points are generically distinct from their ground state counterparts, and represent novel nonequilibrium critical phases of matter.

We use particle-based simulations to examine the static and driven collective phases of Skyrmions interacting with random quenched disorder. We show that nondissipative effects due to the Magnus term reduce the depinning threshold and strongly affect the Skyrmion motion and the nature of the dynamic phases. The quenched disorder causes the Hall angle to become drive dependent in the moving Skyrmion phase, while different flow regimes produce distinct signatures in the transport curves. For weak disorder, the Skyrmions form a pinned crystal and depin elastically, while for strong disorder the system forms a pinned amorphous state that depins plastically. At high drives the Skyrmions can dynamically reorder into a moving crystal, with the onset of reordering determined by the strength of the Magnus term.

We report the use of novel, capacitively terminated coplanar waveguide resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them.

We report on the magnetic structure and ordering of hexagonal ${\mathrm{LuFeO}}_3$ films of variable thickness grown by molecular-beam epitaxy on YSZ (111) and ${\mathrm{Al}}_2{\mathrm{O}}_3$ (0001) substrates. These crystalline films exhibit long-range structural uniformity dominated by the polar $P{6}_{3}cm$ phase, which is responsible for the paraelectric to ferroelectric transition that occurs above 1000 K. Using bulk magnetometry and neutron diffraction, we find that the system orders into a ferromagnetically canted antiferromagnetic state via a single transition below 155 K regardless of film thickness, which is substantially lower than that previously reported in hexagonal ${\mathrm{LuFeO}}_3$ films. The symmetry of the magnetic structure in the ferroelectric state implies that this material is a strong candidate for linear magnetoelectric coupling and control of the ferromagnetic moment directly by an electric field.

Superparamagnetic beads are widely used in biochemistry and single-molecule biophysics, but the nature of the anisotropy that enables the application of torques remains controversial. To quantitatively investigate the torques experienced by superparamagnetic particles, we use a biological motor to rotate beads in a magnetic field and demonstrate that the underlying potential is $\pi$ periodic. In addition, we tether a bead to a single DNA molecule and show that the angular trap stiffness increases nonlinearly with magnetic field strength. Our results indicate that the superparamagnetic beads’ anisotropy derives from a nonuniform intrabead distribution of superparamagnetic nanoparticles.

We report new experimental results obtained on three different laser facilities that show directed laser-driven relativistic electron-positron jets with up to 30 times larger yields than previously obtained and a quadratic ($\sim E_L^2$) dependence of the positron yield on the laser energy. This favorable scaling stems from a combination of higher energy electrons due to increased laser intensity and the recirculation of MeV electrons in the mm-thick target. Based on this scaling, first principles simulations predict the possibility of using such electron-positron jets, produced at upcoming high-energy laser facilities, to probe the physics of relativistic collisionless shocks in the laboratory.

In a recent paper [A. J. Window et al., Phys. Rev. Lett. 107, 016105 (2011)], it was proposed that ${\mathrm{V}}_2{\mathrm{O}}_3(0001)$ is terminated by the so-called ${\mathrm{O}}_3$ termination, a reconstruction with a terminating distorted hexagonal oxygen layer. We show that the surface is terminated by vanadyl ($\mathrm{V}═\mathrm{O}$) groups instead. This conclusion is based on quantitative low-energy electron diffraction combined with scanning tunneling microscopy, fast atom scattering, and density functional theory employing the Heyd-Scuseria-Ernzerhof functional. New insights into the subsurface sensitivity of ion beam triangulation show that results previously interpreted in favor of the ${\mathrm{O}}_3$ termination are reconcilable with vanadyl termination as well.

We introduce a multipartite extension of an information-theoretic distance introduced by Zurek [Nature (London) 341, 119 (1989)]. We use it to develop a new tool for studying quantum correlations from an information-theoretic perspective. In particular, we derive entropic tests of multipartite nonlocality for three qubits and for an arbitrary even number of qubits as well as a test of state-independent contextuality. In addition, we rederive the tripartite Mermin inequality and a state-independent noncontextuality inequality by Cabello [Phys. Rev. Lett. 101, 210401 (2008)]. This suggests that the information-theoretic distance approach to multipartite nonlocality and state-independent contextuality can provide a more general treatment of nonclassical correlations than the orthodox approach based on correlation functions.

We investigate the effect of QCD resummation to kinematical correlations in the Higgs boson plus high transverse momentum ($P_T$) jet events produced at hadron colliders. We show that at the complete one-loop order, the Collins-Soper-Sterman resummation formalism can be applied to derive the Sudakov form factor. We compare the singular behavior of resummation calculation to fixed order prediction in the case that a Higgs boson and high $P_T$ jet are produced nearly back to back in their transverse momenta, and find perfect agreement. The phenomenological importance of the resummation effect at the LHC is also demonstrated.

We perform generalized measurements of a qubit by realizing the qubit as a coin in a photonic quantum walk and subjecting the walker to projective measurements. Our experimental technique can be used to realize, photonically, any rank-1 single-qubit positive-operator-valued measure via constructing an appropriate interferometric quantum-walk network and then projectively measuring the walker’s position at the final step.