We demonstrate single-atom resolution, as well as detection sensitivity more than 20 dB below the quantum projection noise limit, for hyperfine-state-selective measurements on mesoscopic ensembles containing 100 or more atoms. The measurement detects the atom-induced shift of the resonance frequency of an optical cavity containing the ensemble. While spatially varying coupling of atoms to the cavity prevents the direct observation of a quantized signal, the demonstrated measurement resolution provides the readout capability necessary for atomic interferometry substantially below the standard quantum limit and down to the Heisenberg limit.

Colloidal capsules can sustain an external osmotic pressure; however, for a sufficiently large pressure, they will ultimately buckle. This process can be strongly influenced by structural inhomogeneities in the capsule shells. We explore how the time delay before the onset of buckling decreases as the shells are made more inhomogeneous; this behavior can be quantitatively understood by coupling shell theory with Darcy’s law. In addition, we show that the shell inhomogeneity can dramatically change the folding pathway taken by a capsule after it buckles.

The interaction forces between dust grains in a flowing plasma are strongly modified by the formation of ion wakes. Here, we study the interparticle forces mediated by ion wakes in the presence of a strong magnetic field parallel to the ion flow. For increasing magnetic flux densities a continuous decay of the interaction force is observed. This transition occurs at parameters, where the ion cyclotron frequency starts to exceed the ion plasma frequency, which is in agreement with theoretical predictions. The modification of the interparticle forces is important for the understanding of the structure and dynamics of magnetized dusty plasmas.

Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) has been achieved using a biasable limiter which has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and transport in the LAPD. The LAPD rotates spontaneously in the ion diamagnetic direction; positive limiter bias first reduces, then minimizes (producing a near-zero shear state), and finally reverses the flow into the electron diamagnetic direction. Degradation of particle confinement is observed in the minimum shearing state and a reduction in the turbulent particle flux is observed with increasing shearing in both flow directions. Near-complete suppression of the turbulent particle flux is observed for shearing rates comparable to the turbulent autocorrelation rate measured in the minimum shear state. Turbulent flux suppression is dominated by amplitude reduction in low-frequency ($<10\mathrm{kHz}$) density fluctuations. An increase in fluctuations for the highest shearing states is observed with the emergence of a coherent mode which does not lead to net particle transport. The variations of density fluctuations are fit well with power laws and compare favorably to simple models of shear suppression of transport.

The drift kinetic equation is solved for low density TJ-II plasmas employing slowly varying, time-dependent profiles. This allows us to simulate density ramp-up experiments and describe from first principles the formation and physics of the radial electric field shear layer. The main features of the transition are perfectly captured by the calculation, and good quantitative agreement is also found. The results presented here, that should be valid for other nonquasisymmetric stellarators, provide a fundamental explanation for a wealth of experimental observations connected to the shear layer emergence in TJ-II. The key quantity is the neoclassical viscosity, which is shown to go smoothly to zero when the critical density is approached from below. This makes it possible for turbulence-related phenomena, and particularly zonal flows, to arise in the neighborhood of the transition.

When an impurity is doped in a solid, it inevitably induces a local stress, tending to expand or contract the lattice. Consequently, strain can be applied to change the solubility of impurity in a solid. Generally, the solubility responds to strain “monotonically,” increasing (decreasing) with the tensile (compressive) strain if the impurity induces a compressive stress or vice versa. Using first-principles calculations, however, we discovered that the H solubility can be enhanced by anisotropic strain in some bcc metals, almost independent of the sign of strain. This anomalous behavior is found to be caused by a continuous change of H location induced by anisotropic strain. Our finding suggests a cascading effect of H bubble formation in bcc metals: the H solution leads to H bubble formation that induces anisotropic strain that in turn enhances H solubility to further facilitate bubble growth.

We study the phase diagram of the quantum Hall effect in four-dimensional (4D) space. Unlike in 2D, in 4D there exists a metallic as well as an insulating phase, depending on the disorder strength. The critical exponent $\nu \approx 1.2$ of the diverging localization length at the quantum Hall insulator-to-metal transition differs from the semiclassical value $\nu =1$ of 4D Anderson transitions in the presence of time-reversal symmetry. Our numerical analysis is based on a mapping of the 4D Hamiltonian onto a 1D dynamical system, providing a route towards the experimental realization of the 4D quantum Hall effect.

We have investigated the consequences of physical aging in thin spin-coated glassy polystyrene films through detailed dewetting studies. A simultaneous and equally fast exponential decay of dewetting velocity, width, and height of the rim with aging time was observed, which is related to a reduction of residual stresses within such films. The temperature dependence of these decay times followed an Arrhenius behavior, yielding an activation energy of $70\pm 6\mathrm{kJ}/\mathrm{mol}$, on the same order of magnitude as values for the $\beta$-relaxation of polystyrene and for relaxations of surface topographical features. Our results suggest that rearrangements at the level of chain segments are sufficient to partially relax frozen-in out-of-equilibrium local chain conformations, i.e., the cause of residual stresses, and they might also be responsible for macroscopic relaxations at polymer surfaces.

We have spectroscopically investigated the thermally and doping-induced metal-insulator transitions for pyrochlore-type ${\mathrm{Nd}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ as well as its Rh-doped analogs ${\mathrm{Nd}}_2({\mathrm{Ir}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{O}}_7$, where the spin-orbit interaction as well as the electron correlation is effectively tuned by the doping level ($x$). The charge dynamics dramatically changes on an energy scale of 1 eV in the course of thermally and doping-induced metal-insulator transitions, while the insulating ground state shows a small but well-defined charge gap of 45 meV. Anomalous doping variation of the low-energy ($<0.3\mathrm{eV}$) optical-conductivity spectra at the ground state can be interpreted in terms of the phase changes among the narrow-gap Mott insulator, Weyl semimetal, and correlated metal.

We have measured the plasma resonances of an array of Josephson junctions in the regime $E_J\gg E_C$, up to the ninth harmonic by incorporating it as part of a resonator capacitively coupled to a coplanar waveguide. From the characteristics of the resonances, we infer the successful implementation of a superinductance, an electrical element with a nondissipative impedance greater than the resistance quantum [$R_Q=h/(2e{)}^2\simeq 6.5\mathrm{k}\Omega$] at microwave frequencies. Such an element is crucial for preserving the quantum coherence in circuits exploiting large fluctuations of the superconducting phase. Our results show internal losses less than 20 ppm, self-resonant frequencies greater than 10 GHz, and phase-slip rates less than 1 mHz, enabling direct application of such arrays for quantum information and metrology. Arrays with a loop geometry also demonstrate a new manifestation of flux quantization in a dispersive analog of the Little-Parks effect.

We report on the realization of a superinductor, a dissipationless element whose microwave impedance greatly exceeds the resistance quantum $R_Q$. The design of the superinductor, implemented as a ladder of nanoscale Josephson junctions, enables tuning of the inductance and its nonlinearity by a weak magnetic field. The Rabi decay time of the superinductor-based qubit exceeds $1\mu \mathrm{s}$. The high kinetic inductance and strong nonlinearity offer new types of functionality, including the development of qubits protected from both flux and charge noises, fault tolerant quantum computing, and high-impedance isolation for electrical current standards based on Bloch oscillations.

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate twin boundaries in stoichiometric FeSe films grown by molecular beam epitaxy. Twin boundaries can be unambiguously identified by imaging the 90° change in the orientation of local electronic dimers from Fe site impurities on either side. Twin boundaries run at approximately 45° to the Fe-Fe bond directions, and noticeably suppress the superconducting gap, in contrast with the recent experimental and theoretical findings in other iron pnictides. Furthermore, vortices appear to accumulate on twin boundaries, consistent with the degraded superconductivity there. The variation in superconductivity is likely caused by the increased Se height in the vicinity of twin boundaries, providing the first local evidence for the importance of this height to the mechanism of superconductivity.

We investigate the exchange coupling between perpendicular anisotropy (PMA) $\mathrm{Co}/\mathrm{Pt}$ and IrMn in-plane antiferromagnets (AFMs), as well as tunneling anisotropic magnetoresistance (TAMR) in $[\mathrm{Pt}/\mathrm{Co}]/\mathrm{IrMn}/{\mathrm{AlO}}_x/\mathrm{Pt}$ tunnel junctions, where $\mathrm{Co}/\mathrm{Pt}$ magnetization drives rotation of AFM moments with the formation of exchange-spring twisting. When coupled with a PMA ferromagnet, the AFM moments partially rotate with out-of-plane magnetic fields, in contrast with being pinned along the easy direction of IrMn for in-plane fields. Because of the superior thermal tolerance of perpendicular exchange coupling and the stability of moments in $\sim 6\mathrm{nm}$-thick IrMn, TAMR gets significantly enhanced up to room temperature. Their use would advance the process towards practical AFM spintronics.

Deactivation of excited phenanthrene by molecular oxygen is utilized to probe the structural heterogeneity of supercooled propylene carbonate. The diffusion rate of oxygen molecules in different regions varies over two orders of magnitude. The size of the regions of different oxygen mobility was determined to be 1.5 nm. Values from 0.2 to 30 s have been obtained for the lifetime of these regions over a temperature range from $T_g-1$ to $T_g+4\mathrm{K}$ ($T_g=158\mathrm{K}$). The heterogeneity lifetime is in close agreement with the $\alpha$-relaxation time determined by dielectric spectroscopy. The obtained results argue in favor of the statement that the heterogeneous cooperative dynamics of host molecules (so-called dynamical heterogeneity) is of structural origin.

Many populations in nature are fragmented: they consist of local populations occupying separate patches. A local population is prone to extinction due to the shot noise of birth and death processes. A migrating population from another patch can dramatically delay the extinction. What is the optimal migration rate that minimizes the extinction risk of the whole population? Here, we answer this question for a connected network of model habitat patches with different carrying capacities.

Polymeric nanoparticles (NPs) have great application potential in science and technology. Their functionality strongly depends on their size. We present a theory for the size of NPs formed by precipitation of polymers into a bad solvent in the presence of a stabilizing surfactant. The analytical theory is based upon diffusion-limited coalescence kinetics of the polymers. Two relevant time scales, a mixing and a coalescence time, are identified and their ratio is shown to determine the final NP diameter. The size is found to scale in a universal manner and is predominantly sensitive to the mixing time and the polymer concentration if the surfactant concentration is sufficiently high. The model predictions are in good agreement with experimental data. Hence the theory provides a solid framework for tailoring NPs with a priori determined size.

Current methods for evaluating solar cell efficiencies cannot be applied to low-dimensional structures where phenomena from the realm of near-field optics prevail. We present a theoretical approach to analyze solar cell performance by allowing rigorous electromagnetic calculations of the emission rate using the fluctuation-dissipation theorem. Our approach shows the direct quantification of the voltage, current, and efficiency of low-dimensional solar cells. This approach is demonstrated by calculating the voltage and the efficiency of a GaAs slab solar cell for thicknesses from several microns down to a few nanometers. This example highlights the ability of the proposed approach to capture the role of optical near-field effects in solar cell performance.

We realize and study an attractively interacting two-dimensional Fermi liquid. Using momentum-resolved photoemission spectroscopy, we measure the self-energy, determine the contact parameter of the short-range interaction potential, and find their dependence on the interaction strength. We successfully compare the measurements to a theoretical analysis, properly taking into account the finite temperature, harmonic trap, and the averaging over several two-dimensional gases with different peak densities.

The first observation of the decay $B^0\to {\overline{D}}^0{K}^{+}{K}^{-}$ is reported from an analysis of $0.62{\mathrm{fb}}^{-1}$ of $pp$ collision data collected with the LHCb detector. Its branching fraction is measured relative to that of the topologically similar decay $B^0\to {\overline{D}}^0{\pi }^{+}{\pi }^{-}$ to be $\frac{\mathcal{B}(B^0\to {\overline{D}}^0{K}^{+}{K}^{-})}{\mathcal{B}(B^0\to {\overline{D}}^0{\pi }^{+}{\pi }^{-})}=0.056\pm 0.011\pm 0.007,$where the first uncertainty is statistical and the second is systematic. The significance of the signal is $5.8\sigma$. Evidence, with $3.8\sigma$ significance, for $B_s^0\to {\overline{D}}^0{K}^{+}{K}^{-}$ decays is also presented. The relative branching fraction is measured to be $\frac{\mathcal{B}(B_s^0\to {\overline{D}}^0{K}^{+}{K}^{-})}{\mathcal{B}(B^0\to {\overline{D}}^0{K}^{+}{K}^{-})}=0.90\pm 0.27\pm 0.20.$ These channels are of interest to study the mechanisms behind hadronic $B$ decays, and open new possibilities for $CP$ violation analyses with larger data sets.

The ${\Theta }^{+}$ pentaquark baryon was searched for via the ${\pi }^{-}p\to K^{-}X$ reaction with a missing mass resolution of $1.4\mathrm{MeV}/c^2$ (FWHM) at the Japan Proton Accelerator Research Complex (J-PARC). ${\pi }^{-}$ meson beams were incident on the liquid hydrogen target with a beam momentum of $1.92\mathrm{GeV}/c$. No peak structure corresponding to the ${\Theta }^{+}$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2° to 15° in the laboratory frame is obtained to be $0.26\mu \mathrm{b}/\mathrm{sr}$ in the mass region of $1.51–1.55\mathrm{GeV}/c^2$. The upper limit of the ${\Theta }^{+}$ decay width is obtained to be 0.72 and 3.1 MeV for $J_{\Theta }^P=1/2^{+}$ and $J_{\Theta }^P=1/2^{-}$, respectively, using the effective Lagrangian approach.