Local structural excitations in model glasses

Structural excitations of model Lennard-Jones glass systems are investigated using the Activation-Relaxation-Technique (ART), which explores the potential energy landscape of a local minimum energy configuration by converging to a nearby saddle-point configuration. Performing ART results in a distribution of barrier energies that is single-peaked for well relaxed samples. The present work characterises such atomic scale excitations in terms of their local structure and environment. It is found that, at zero applied stress, many of the identified events consist of chain-like excitations that can either be extended or ring-like in their geometry. The location and activation energy of these saddle-point structures are found to correlate with the type of atom involved, and with spatial regions that have low shear moduli and are close to the excess free volume within the configuration. Such correlations are however weak and more generally the identified local structural excitations are seen to exist throughout the model glass sample. The work concludes with a discussion within the framework of $\alpha$ and $\beta$ relaxation processes that are known to occur in the under-cooled liquid regime.Comment: 34 Pages, 13 Figure

Four-photon orbital angular momentum entanglement

Quantum entanglement shared between more than two particles is essential to foundational questions in quantum mechanics, and upcoming quantum information technologies. So far, up to 14 two-dimensional qubits have been entangled, and an open question remains if one can also demonstrate entanglement of higher-dimensional discrete properties of more than two particles. A promising route is the use of the photon orbital angular momentum (OAM), which enables implementation of novel quantum information protocols, and the study of fundamentally new quantum states. To date, only two of such multidimensional particles have been entangled albeit with ever increasing dimensionality. Here we use pulsed spontaneous parametric downconversion (SPDC) to produce photon quadruplets that are entangled in their OAM, or transverse-mode degrees of freedom; and witness genuine multipartite Dicke-type entanglement. Apart from addressing foundational questions, this could find applications in quantum metrology, imaging, and secret sharing.Comment: 5 pages, 4 figure

Sub-nanometer free electrons with topological charge

The holographic mask technique is used to create freely moving electrons with quantized angular momentum. With electron optical elements they can be focused to vortices with diameters below the nanometer range. The understanding of these vortex beams is important for many applications. Here we present a theory of focused free electron vortices. The agreement with experimental data is excellent. As an immediate application, fundamental experimental parameters like spherical aberration and partial coherence are determined.Comment: 4 pages, 5 figure

Magnetic thermodynamics as proxy for chemical inhomogeneity in hemo-ilmenite solid solutions: A dynamic ac susceptibility study

In this study, we present ac susceptibility measurements for a synthetic and a natural hemo-ilmenite (HI) solid solution (x)FeTiO3-(1−x)Fe2O3 with compositions x=0.87(1) and 0.88(8), respectively. The focus of the investigation is the magnetic ordering at the Curie temperature T C and the spin-glass-like freezing at the freezing temperature T f. The sharpness of T C for the synthetic solid solution with well-defined structure indicates the chemical homogeneity of the solution, whereas the disperse magnetic ordering of the natural solid solution reveals inhomogeneities described as spin glass system ofvariations in composition x. The frequency dispersion of T f was determined between 10Hz and 10kHz and was found to obey a dynamic scaling power law. The relaxation rates deviate by five orders of magnitude where the synthetic solid solution exhibits ω0=3(1)×104Hz and the natural one 5.5×109Hz. The strong deviation is attributed to the difference in the ordered state above T f. These findings provide an insight into the cooling-rate effects of natural solid solutions and how magnetic thermodynamics can be used to probe the chemical homogeneity of such system

Fe-Ti-O exchange at high temperature and thermal hysteresis

In this study, the Fe-Ti-O exchange behaviour between the systems hemo-ilmenite (y)FeTiO3-(1 −y)Fe2O3 and titano-magnetite (x)Fe2TiO4-(1 −x)Fe3O4 was investigated in the temperature range from 900 to 1400 K in an inert Ar atmosphere. Starting from a mixture of hematite and ilmenite with a fixed mol per cent, heat treatment generates a self-adjusting chemical equilibrium between hemo-ilmenite and titano-magnetite solid solution by means of interdiffusion and Fe3+→ Fe2+ reduction. Structural and magnetic characterization reveals that hemo-ilmenite is stable at all temperatures, whereas titano-magnetite shows increasing Ti-content with increasing treatment temperature. Heating-cooling cycles were performed for a sample to mimic slow cooling and study its effects on the two solid solutions. The magnetic properties of that sample exhibit thermal hysteresis during these cycles, as the Ti departs from titano-magnetite and thus leads to a new chemical equilibrium. The experimental data provide insight into the dynamics of the formation of Fe-Ti-O phases formed under varying conditions in geological system

Fiber transport of spatially entangled photons

Entanglement in the spatial degrees of freedom of photons is an interesting resource for quantum information. For practical distribution of such entangled photons it is desireable to use an optical fiber, which in this case has to support multiple transverse modes. Here we report the use of a hollow-core photonic crystal fiber to transport spatially entangled qubits.Comment: 4 pages, 4 figure

A hybrid camphor-camphene wax material for studies on self-propelled motion.

A new material that combines self-propelled motion with wax-like mechanical properties and can be formed into non-trivial shapes is presented