We report results of ab initio electronic structure and quantum conductance calculations indicating the emergence of conduction at the surface of semiconducting carbon foams. The occurrence of new conduction states is intimately linked to the topology of the surface and not limited to foams of elemental carbon. Our interpretation based on rehybridization theory indicates that conduction in the foam derives from first- and second-neighbor interactions between $p_{\parallel }$ orbitals lying in the surface plane, which are related to $p_{\perp }$ orbitals of graphene. The topologically protected conducting state occurs on bare and hydrogen-terminated foam surfaces and is thus unrelated to dangling bonds. Our results for carbon foam indicate that the conductance behavior may be further significantly modified by surface patterning.

Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. In this Letter, we combine these two approaches to study the dynamics of a superconducting phase qubit. We experimentally demonstrate Landau-Zener interferometry based on the pure geometric phases in this solid-state qubit. We observe the interference caused by a pure geometric phase accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is canceled out by a spin-echo pulse. The full controllability of the qubit state as a function of the intrinsically robust geometric phase provides a promising approach for quantum state manipulation.

We present results from small-angle x-ray scattering data on the effect of high pressure on the phase behavior of dense lysozyme solutions in the liquid-liquid phase separation region, and characterize the underlying intermolecular protein-protein interactions as a function of temperature and pressure in this region of phase space. A reentrant liquid-liquid phase separation region has been discovered at elevated pressures, which originates in the pressure dependence of the solvent-mediated protein-protein interactions.

Molecular two-center interferences in a collision induced excitation of ${\mathrm{H}}_2^{+}$ projectile ions, with simultaneous ionization of helium target atoms, are investigated in a kinematically complete experiment. In the process under investigation, the helium atom is singly ionized and simultaneously the molecular hydrogen ion is dissociated. Different collision mechanisms are identified and interference fringes emerging from a correlated first-order mechanism and from an independent second-order process are observed.

Trapping of mesoscopic particles by optical forces usually relies on the gradient force, whereby particles are attracted into optical wells formed by landscaping the intensity of an optical field. This is most often achieved by optical Gaussian beams, interference patterns, general phase contrast methods, or other mechanisms. Hence, although the simultaneous trapping of several hundreds of particles can be achieved, these particles remain mostly independent with negligible interaction. Optical matter, however, relies on close packing and binding forces, with fundamentally different electrodynamic properties. In this Letter, we build ensembles of optically bound particles to realize a reflective surface that can be used to image an object or to focus a light beam. To our knowledge, this is the first experimental proof of the creation of a mirror by optical matter, and represents an important step toward the realization of a laser-trapped mirror (LTM) in space. From a theoretical point of view, optically bound close packing requires an exact solver of Maxwell’s equations in order to precisely compute the field scattered by the collection of particles. Such rigorous calculations have been developed and are used here to study the focusing and resolving power of an LTM.

Using exact numerical techniques, we investigate the nature of excitonic (electron-hole) bound states and the development of exciton coherence in the one-dimensional half-filled extended Falicov-Kimball model. The ground-state phase diagram of the model exhibits, besides band-insulator and staggered orbital ordered phases, an excitonic insulator (EI) with power-law correlations. The criticality of the EI state shows up in the von Neumann entropy. The anomalous spectral function and condensation amplitude provide the binding energy and coherence length of the electron-hole pairs which, on their part, point towards a Coulomb interaction driven crossover from BCS-like electron-hole pairing fluctuations to tightly bound excitons. We show that while a mass imbalance between electrons and holes does not affect the location of the BCS-BEC crossover regime, it favors staggered orbital ordering to the disadvantage of the EI. Within the Bose-Einstein condensation (BEC) regime, the quasiparticle dispersion develops a flat valence-band top, in accord with the experimental finding for ${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$.

A bimolecular synthetic reaction (imine synthesis) was performed compartmentalized in micrometer-diameter emulsion droplets. The apparent equilibrium constant ($K_{\mathrm{eq}}$) and apparent forward rate constant ($k_1$) were both inversely proportional to the droplet radius. The results are explained by a noncatalytic reaction-adsorption model in which reactants adsorb to the droplet interface with relatively low binding energies of a few $k_{B}T$, react and diffuse back to the bulk. Reaction thermodynamics is therefore modified by compartmentalization at the mesoscale—without confinement on the molecular scale—leading to a universal mechanism for improving unfavorable reactions.

Quantum physics allows for unconditionally secure communication between parties that trust each other. However, when the parties do not trust each other such as in the bit commitment scenario, quantum physics is not enough to guarantee security unless extra assumptions are made. Unconditionally secure bit commitment only becomes feasible when quantum physics is combined with relativistic causality constraints. Here we experimentally implement a quantum bit commitment protocol with relativistic constraints that offers unconditional security. The commitment is made through quantum measurements in two quantum key distribution systems in which the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. In each run of the experiment, a bit is successfully committed with less than $5.68\times 10^{-2}$ cheating probability. This demonstrates the experimental feasibility of quantum communication with relativistic constraints.

We propose a method for universal fault-tolerant quantum computation using concatenated quantum error correcting codes. The concatenation scheme exploits the transversal properties of two different codes, combining them to provide a means to protect against low-weight arbitrary errors. We give the required properties of the error correcting codes to ensure universal fault tolerance and discuss a particular example using the 7-qubit Steane and 15-qubit Reed-Muller codes. Namely, other than computational basis state preparation as required by the DiVincenzo criteria, our scheme requires no special ancillary state preparation to achieve universality, as opposed to schemes such as magic state distillation. We believe that optimizing the codes used in such a scheme could provide a useful alternative to state distillation schemes that exhibit high overhead costs.

The first measurement of the helicity dependence of the photoproduction cross section of single neutral pions off protons is reported for photon energies from 600 to 2300 MeV, covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, and BnGa partial wave analyses. Strikingly large differences between data and predictions are observed, which are traced to differences in the helicity amplitudes of well-known and established resonances. Precise values for the helicity amplitudes of several resonances are reported.

We consider the optical properties of a gas of molecules that are brought to fast unidirectional spinning by a pulsed laser field. It is shown that a circularly polarized probe light passing through the medium inverts its polarization handedness and experiences a frequency shift controllable by the sense and the rate of molecular rotation. Our analysis is supported by two recent experiments on the laser-induced rotational Doppler effect in molecular gases and provides a good qualitative and quantitative description of the experimental observations.

In this Letter we address the issue of how synthetic spin-orbit (SO) coupling can strongly affect three-body physics in ultracold atomic gases. We consider a system which consists of three fermionic atoms, including two spinless heavy atoms and one spin-$1/2$ light atom subjected to an isotropic SO coupling. We find that SO coupling can induce universal three-body bound states with a negative $s$-wave scattering length at a smaller mass ratio, where no trimer bound state can exist if in the absence of SO coupling. The energies of these trimers are independent of the high-energy cutoff, and therefore they are universal ones. Moreover, the resulting atom-dimer resonance can be effectively controlled by SO coupling strength. Our results can be applied to systems like a ${}^6\mathrm{Li}$ and ${}^{40}\mathrm{K}$ mixture.

We study the genesis and the selective propagation of complex crack networks induced by thermal shock or drying of brittle materials. We use a quasistatic gradient damage model to perform large-scale numerical simulations showing that the propagation of fully developed cracks follows Griffith criterion and depends only on the fracture toughness, while crack morphogenesis is driven by the material’s internal length. Our numerical simulations feature networks of parallel cracks and selective arrest in two dimensions and hexagonal columnar joints in three dimensions, without any hypotheses on cracks geometry, and are in good agreement with available experimental results.

Subdiffraction optical microscopy allows the imaging of cellular and subcellular structures with a resolution finer than the diffraction limit. Here, combining the absorption-based photoacoustic effect and intensity-dependent photobleaching effect, we demonstrate a simple method for subdiffraction photoacoustic imaging of both fluorescent and nonfluorescent samples. Our method is based on a double-excitation process, where the first excitation pulse partially and inhomogeneously bleaches the molecules in the diffraction-limited excitation volume, thus biasing the signal contributions from a second excitation pulse striking the same region. The differential signal between the two excitations preserves the signal contribution mostly from the center of the excitation volume, and dramatically sharpens the lateral resolution. Moreover, due to the nonlinear nature of the signal, our method offers an inherent optical sectioning capability, which is lacking in conventional photoacoustic microscopy. By scanning the excitation beam, we performed three-dimensional subdiffraction imaging of varied fluorescent and nonfluorescent species. As any molecules have absorption, this technique has the potential to enable label-free subdiffraction imaging, and can be transferred to other optical imaging modalities or combined with other subdiffraction methods.

Water and oil repellent coatings—so-called superamphiphobic coatings—greatly reduce the interaction between a liquid and a solid. So far, only flat or weakly curved superhydrophobic and superamphiphobic surfaces have been designed. This raises the question of whether highly curved structures or microspheres are feasible. Therefore, we coated microspheres with a superamphiphobic layer and measured the force between the spheres and a liquid. A qualitatively different dependence of the adhesion force on the applied load for superamphiphobic and smooth spheres is detected. Furthermore, we demonstrate both experimentally and theoretically that superamphiphobicity fails below a critical particle radius, depending on topological details and type of liquid. Therefore, this study sets a fundamental physical limit to the application of superamphiphobic layers for small objects with high curvature.

The ratio of orbital ($L$) and spin ($S$) contributions to the magnetically ordered moments of a $5d$ transition metal oxide, $\mathrm{Sr}{}_2\mathrm{IrO}{}_4$ was evaluated by nonresonant magnetic x-ray diffraction. We applied an improved experimental setting that minimized the experimental error, in which we varied only the linear polarization of incident x ray at a fixed scattering angle. Strong polarization dependence of the intensity of magnetic diffraction was observed, from which we conclude that the ordered moments contain substantial contribution from the orbital degree of freedom with the ratio of $⟨L⟩/⟨S⟩\sim 5.0$, evidencing the pronounced effect of spin-orbit coupling. The obtained ratio is close to, but slightly larger than the expected value for the ideal $J_{\mathrm{eff}}=1/2$ moment of a spin-orbital Mott insulator, $|⟨J_{1/2}|L_z|J_{1/2}⟩|/|⟨J_{1/2}|S_z|J_{1/2}⟩|=4$, which cannot be accounted for by the redistribution of orbital components within the $t_{2g}$ bands associated with the elongation of the $\mathrm{IrO}{}_6$ octahedra.

A 4-parameter Fermi-liquid calculation of the high-$T_c$ cuprate phase diagram is reported. Simultaneously accounted for are the special doping densities of 5% and 16%, the $d$-wave functional form of the (orbital antiferromagnetic) pseudogap, the measured $T_c$, superconducting gap, pseudogap and superfluid density as a function of doping, the particle-hole doping asymmetry and the half-filling spin wave velocity.

As established in the very early work of Edwin Hall, ferromagnetic conductors have an anomalous Hall conductivity contribution that cannot be attributed to Lorentz forces and therefore survives in the absence of a magnetic field. These anomalous Hall conductivities are normally assumed to be proportional to magnetization. We use symmetry arguments and first-principles electronic structure calculations to counter this assumption and to predict that ${\mathrm{Mn}}_3\mathrm{Ir}$, a high-temperature antiferromagnet that is commonly employed in spin-valve devices, has a large anomalous Hall conductivity.

The recent years have witnessed an emergence of the field of all-spin-based devices without any flow of charge. An ultimate goal of this scientific direction is the realization of the full spectrum of spin-based networks as in modern electronics. The concept of energy-storing elements, indispensable for those networks, are so far lacking. Analyzing analytically the size dependent properties of magnetic chains that are coupled via either exchange or long-range dipolar or Ruderman-Kittel-Kasuya-Yosida interactions, we discover a particularly simple law: magnetic configurations corresponding to helices with integer number of twists, which are commensurate with the chain’s length, are energetically stable. This finding, supported by simulations and an experimentally benchmarked model, agrees with the study [R. Skomski et al., J. Appl. Phys. 111, 07E116 (2012)] showing that boundaries can topologically stabilize structures that are not stable otherwise. On that basis, an energy-storing element that uses spin at every stage of its operation is proposed.

We study vanadium spinels $A{\mathrm{V}}_2{\mathrm{O}}_4(A=\mathrm{Cd},\mathrm{Mg})$ in pulsed magnetic fields up to 65 T. A jump in magnetization at ${\mu }_{0}H\approx 40\mathrm{T}$ is observed in the single-crystal $\mathrm{Mg}{\mathrm{V}}_2{\mathrm{O}}_4$, indicating a field induced quantum phase transition between two distinct magnetic orders. In the multiferroic $\mathrm{Cd}{\mathrm{V}}_2{\mathrm{O}}_4$, the field induced transition is accompanied by a suppression of the electric polarization. By modeling the magnetic properties in the presence of strong spin-orbit coupling characteristic of vanadium spinels, we show that both features of the field induced transition can be successfully explained by including the effects of the local trigonal crystal field.