Electrons surfing on a sound wave as a platform for quantum optics with flying electrons

Electrons in a metal are indistinguishable particles that strongly interact with other electrons and their environment. Isolating and detecting a single flying electron after propagation to perform quantum optics like experiments at the single electron level is therefore a challenging task. Up to date, only few experiments have been performed in a high mobility two-dimensional electron gas where the electron propagates almost ballistically. Flying electrons were detected via the current generated by an ensemble of electrons and electron correlations were encrypted in the current noise. Here we demonstrate the experimental realisation of high efficiency single electron source and single electron detector for a quantum medium where a single electron is propagating isolated from the other electrons through a one-dimensional channel. The moving potential is excited by a surface acoustic wave, which carries the single electron along the 1D-channel at a speed of 3\mum/ns. When such a quantum channel is placed between two quantum dots, a single electron can be transported from one quantum dot to the other, which is several micrometres apart, with a quantum efficiency of emission and detection of 96% and 92%, respectively. Furthermore, the transfer of the electron can be triggered on a timescale shorter than the coherence time T2* of GaAs spin qubits6. Our work opens new avenues to study the teleportation of a single electron spin and the distant interaction between spatially separated qubits in a condensed matter system.Comment: Total 25 pages. 12 pages main text, 4 figures, 5 pages supplementary materia

Entanglement or separability: The choice of how to factorize the algebra of a density matrix

We discuss the concept of how entanglement changes with respect to different factorizations of the total algebra which describes the quantum states. Depending on the considered factorization a quantum state appears either entangled or separable. For pure states we always can switch unitarily between separability and entanglement, however, for mixed states a minimal amount of mixedness is needed. We discuss our general statements in detail for the familiar case of qubits, the GHZ states, Werner states and Gisin states, emphasizing their geometric features. As theorists we use and play with this free choice of factorization, which is naturally fixed for an experimentalist. For theorists it offers an extension of the interpretations and is adequate to generalizations, as we point out in the examples of quantum teleportation and entanglement swapping.Comment: 29 pages, 9 figures. Introduction, Conclusion and References have been extended in v

Structure, electrical conductivity and oxygen transport properties of Ruddlesden–Popper phases Lnn+1NinO3n+1 (Ln = La, Pr and Nd; n = 1, 2 and 3)

Layered Ruddlesden–Popper (RP) lanthanide nickelates, Lnn+1NinO3n+1 (Ln = La, Pr and Nd; n = 1, 2 and 3), are considered potential cathode materials in solid oxide fuel cells. In this study, the thermal evolution of the structure, oxygen nonstoichiometry, electrical conductivity and oxygen transport properties of La2NiO4+δ, Nd2NiO4+δ, La3Ni2O7−δ, La4Ni3O10−δ, Pr4Ni3O10−δ and Nd4Ni3O10−δ are investigated. Phase transitions involving a disruption of the cooperative tilting of the perovskite layers in the low-temperature structure thereby transforming it to a more symmetric structure are observed in several of the materials upon heating in air. Pr4Ni3O10−δ and Nd4Ni3O10−δ show no phase transition from room temperature up to 1000 °C. High density ceramics (>96%) are obtained after sintering at 1300 °C and (for n = 2 and n = 3 members) post-sintering annealing at reduced temperatures. Data for the electrical conductivity measurements on these specimens indicate itinerant behaviour of the charge carriers in the RP nickelates. The increase in p-type conductivity with the order n of the RP phase is interpreted as arising from the concomitant increase in the formal valence of Ni. The observations can be interpreted in terms of a simple energy band scheme, showing that electron holes are formed in the σx2−y2↑ band upon increasing the oxidation state of Ni. Electrical conductivity relaxation measurements reveal remarkable similarities between the surface exchange coefficients (kchem) of the different RP phases despite the differences in the order parameter n and the nature of the lanthanide ion. Calculation of the oxygen self-diffusion coefficients (Ds) from the experimental values of the chemical diffusion coefficients (Dchem), using the corresponding data of oxygen non-stoichiometry from thermogravimetry measurements, shows that these are strongly determined by the order parameter n. The value of Ds decreases almost one order of magnitude on going from the n = 1 members La2NiO4+δ and Nd2NiO4+δ to the n = 2 member La3Ni2O7−δ, and again one order of magnitude on going to the n = 3 members La4Ni3O10−δ, Pr4Ni3O10−δ and Nd4Ni3O10−δ. The results confirm that oxygen-ion transport in the investigated RP nickelates predominantly occurs via an interstitialcy mechanism within the rock-salt layer of the structures

A modified thermo-mechanical modeling approach for shape memory alloy behaviour13;

The Brinson-Lammering constitutive model is modified to account for the nonlinear shape memory alloy behaviour. The model is divided into three modules by keeping each of the three parameters of stress, strain and temperature constant. Experiments were conducted with a NiTiCu material to obtain the model constants. The constants were then incorporated in the model and the behaviour predicted. A good correlation is obtained between the theory and experiments.13

Measures to Reduce the N2O Formation at Perovskite-Based Lean NOx Trap Catalysts under Lean Conditions

The net oxidising atmosphere of lean burn engines requires a special after-treatment catalyst for NOx removal from the exhaust gas. Lean NOx traps (LNT) are such kind of catalysts. To increase the efficiency of LNTs at low temperatures platinised perovskite-based infiltration composites La0.5Sr0.5Fe1-xMxO3-δ/Al2O3 with M = Nb, Ti, Zr have been developed. In general, platinum based LNT catalysts show an undesired, hazardous formation of N2O in the lean operation mode due to a competing C3H6-selective catalytic reduction (SCR) at the platinum sites. To reduce N2O emissions an additional Rh-coating, obtained by incipient wetness impregnation, besides the Pt coating and a two-layered oxidation catalyst (2 wt.% Pd/20 wt.% CeO2/alumina)-LNT constitution, has been investigated. Though the combined Rh-Pt coating shows a slightly increased NOx storage capacity (NSC) at temperatures above 300 °C, it does not decrease N2O formation. The layered oxidation catalyst-LNT system shows a decrease in N2O formation of up to 60% at 200 °C, increasing the maximum NSC up to 176 µmol/g. Furthermore, the NSC temperature range is broadened compared to that of the pure LNT catalyst, now covering a range of 250–300 °C

Phase related oxygen permeation through Sr-doped LaCoO3-δ

Oxygen permeation results through La1-xSrxCoO3-δ are reported. It is shown that in the temperature region 750 - 775 °C an order-disorder of the oxygen sublattice occurs. The low temperature ordered phase is studied by X-Ray powder diffraction (XRD), neutron diffraction as well as selected area electron diffraction (SAED) together with High Resolution Transmission Electron Microscopy (HRTEM) coupled with Parallel Electron Energy Loss Spectroscopy (PEELS) and Energy Dispersive X-Ray spectroscopy (EDX). Although the long range methods XRD and neutron diffraction showed no indications for an oxygen vacancy ordering, SAED and HRTEM showed micro domains exhibiting an ac x ac x 2ac superstructure, along with regions without indications for a superstructure. The superstructure could be interpreted in terms of an oxygen vacancy ordering due to which a large part of the oxygen vacancies were trapped in regions with the superstructure and so effectively reducing the ionic conductivity. By means of PEELS it was shown that the cobalt ions within the superstructure regions have a higher oxidation state than the cobalt ions in the non-ordered regions

Structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1−x−yTixFeyO3−δ

Calcium manganite-based perovskite-type oxides hold promise for application in chemical looping combustion processes and oxygen transport membranes. In this study, we have investigated the structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1−x−yTixFeyO3−δ. Distinct from previous work, data of high-temperature X-ray diffraction (HT-XRD) in the temperature range 600–1000 °C (with intervals of 25 °C) demonstrates that CaMnO3−δ (CM) transforms from orthorhombic to a mixture of orthorhombic and tetragonal phases between 875 °C and 900 °C. Rietveld refinements show the formation of a pure tetragonal phase at 975 °C and of a pure cubic phase at 1000 °C. Partial substitution of manganese by iron and/or titanium to yield CaMn0.875Ti0.125O3−δ (CMT), CaMn0.85Fe0.15O3−δ (CMF) or CaMn0.725Ti0.125Fe0.15O3−δ (CMTF) leads to different phase behaviours. While CMT remains orthorhombic up to the highest temperature covered by the HT-XRD experiments, CMF and CMTF undergo an orthorhombic → tetragonal → cubic sequence of phase transitions. Electrical conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and the surface exchange coefficient (kchem) of the materials. The results demonstrate that oxygen transport is hindered in the tetragonal phase, when occurring, which is attributed to a possible ordering of oxygen vacancies. The small polaron electrical conductivity of CM in the cited temperature range is lowered upon partial manganese substitution, by about 10% for CMF and up to half an order of magnitude for CMT and CMTF

Structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1−x−yTixFeyO3−δ

Calcium manganite-based perovskite-type oxides hold promise for application in chemical looping combustion processes and oxygen transport membranes. In this study, we have investigated the structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1−x−yTixFeyO3−δ. Distinct from previous work, data of high-temperature X-ray diffraction (HT-XRD) in the temperature range 600–1000 °C (with intervals of 25 °C) demonstrates that CaMnO3−δ (CM) transforms from orthorhombic to a mixture of orthorhombic and tetragonal phases between 875 °C and 900 °C. Rietveld refinements show the formation of a pure tetragonal phase at 975 °C and of a pure cubic phase at 1000 °C. Partial substitution of manganese by iron and/or titanium to yield CaMn0.875Ti0.125O3−δ (CMT), CaMn0.85Fe0.15O3−δ (CMF) or CaMn0.725Ti0.125Fe0.15O3−δ (CMTF) leads to different phase behaviours. While CMT remains orthorhombic up to the highest temperature covered by the HT-XRD experiments, CMF and CMTF undergo an orthorhombic → tetragonal → cubic sequence of phase transitions. Electrical conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and the surface exchange coefficient (kchem) of the materials. The results demonstrate that oxygen transport is hindered in the tetragonal phase, when occurring, which is attributed to a possible ordering of oxygen vacancies. The small polaron electrical conductivity of CM in the cited temperature range is lowered upon partial manganese substitution, by about 10% for CMF and up to half an order of magnitude for CMT and CMTF

Effect of Fe content on atomic and electronic structure of complex oxides Sr(Ti,Fe)O3−δ_{3−δ}

We present a study of the electronic and atomic structure of two series of SrTi1 − xFexO3 − δ (STFO) powders with different Fe content produced by two different methods, spray pyrolysis or modified Pechini synthesis, by means of soft X-ray absorption spectroscopy. Partial substitution of Ti by Fe atoms in SrTiO3 were found to cause asymmetric distortion of TiO6 octahedrons, which increases with increasing Fe content that may violate the cubic symmetry of STFO. The presence mainly of Fe3 + states in octahedral environment at small concentration of Fe atoms along with essentially smaller content of Fe4 + states in octahedral environment where the latter contribution increases with increasing Fe content was traced. It is found that the modified Pechini method allows to synthesize more stable structures but a tendency of the SrOx formation in the structure prepared by this technique was marked. The spray pyrolysis method gives the structure free of SrO precipitates but the presence of Fe3 + states in tetrahedral environment with Fe content higher than 50% and even a certain amount of Fe2 + ions in an octahedral environment at concentrations higher than 75% in the STFO prepared by this method was established. The O1s (K)-absorption spectra point to increase in oxygen vacancy concentration with increasing Fe content. The lowest degree of structure distortions with enough high oxygen vacancy concentration was traced in STFO (x = 0.25 to x = 0.35) produced by modified Pechini synthesis, which makes it mostly appropriate for technical applications, e.g., as gas sensors, oxygen separation membranes or as fuel cell material