Überprüfung der Bezugskurven der Schweizer Version des Freiburger Zahlen- und Einsilbertests

Zusammenfassung: Hintergrund: Die Schweizer Ausgabe des Freiburger Sprachverständlichkeitstests unterscheidet sich von der deutschen Version u.a. durch den Ersatz von 5 in der Schweiz ungebräuchlichen einsilbigen Testworten. Zudem wird keine Freifeldentzerrung benutzt und die die sich aus dem Freifeldübertragungsmaß ergebende Differenz von 6dB zwischen Lautsprecher und Kopfhörer wird bei der Kalibrierung nicht berücksichtigt. Der vor einiger Zeit eingeführte Pegelausgleich zwischen den Prüfworten und Anpassungen in der Kalibrierung veranlassten uns zur Überprüfung der Bezugskurven. Patienten/Methoden: Bei 20 normal hörenden Versuchpersonen wurde das Sprachverstehen von Zahlen und einsilbigen Wörtern mit Kopfhörern und Lautsprechern geprüft. Ergebnisse: Der Pegel für 50% Sprachverstehen lag bei Lautsprecherdarbietung im Mittel um 7,5dB niedriger ist als bei Kopfhörerdarbietung. Die mittlere Pegeldifferenz zwischen Zahlen und Einsilbern betrug 9,6dB, liegt also deutlich unter den 14dB der heute in der Schweiz empfohlenen Bezugskurven. Fazit: Die heute in der Schweiz empfohlenen Bezugskurven stimmen für Einsilber bei Kopfhörerdarbietung gut mit unseren Messungen überein, nicht aber für Zahlen und bei Lautsprecherdarbietun

The quantized Hall conductance of a single atomic wire: A proposal based on synthetic dimensions

We propose a method by which the quantization of the Hall conductance can be directly measured in the transport of a one-dimensional atomic gas. Our approach builds on two main ingredients: (1) a constriction optical potential, which generates a mesoscopic channel connected to two reservoirs, and (2) a time-periodic modulation of the channel, specifically designed to generate motion along an additional synthetic dimension. This fictitious dimension is spanned by the harmonic-oscillator modes associated with the tightly-confined channel, and hence, the corresponding "lattice sites" are intimately related to the energy of the system. We analyze the quantum transport properties of this hybrid two-dimensional system, highlighting the appealing features offered by the synthetic dimension. In particular, we demonstrate how the energetic nature of the synthetic dimension, combined with the quasi-energy spectrum of the periodically-driven channel, allows for the direct and unambiguous observation of the quantized Hall effect in a two-reservoir geometry. Our work illustrates how topological properties of matter can be accessed in a minimal one-dimensional setup, with direct and practical experimental consequences.

Ladder approximation to spin velocities in quantum wires

The spin sector of charge-spin separated single mode quantum wires is studied, accounting for realistic microscopic electron-electron interactions. We utilize the ladder approximation (LA) to the interaction vertex and exploit thermodynamic relations to obtain spin velocities. Down to not too small carrier densities our results compare well with existing quantum Monte-Carlo (QMC) data. Analyzing second order diagrams we identify logarithmically divergent contributions as crucial which the LA includes but which are missed, for example, by the self-consistent Hartree-Fock approximation. Contrary to other approximations the LA yields a non-trivial spin conductance. Its considerably smaller computational effort compared to numerically exact methods, such as the QMC method, enables us to study overall dependences on interaction parameters. We identify the short distance part of the interaction to govern spin sector properties.Comment: 6 pages, 6 figures, to appear in Physical Review

Exchange interaction in quantum rings and wires in the Wigner-crystal limit

We present a controlled method for computing the exchange coupling in correlated one-dimensional electron systems based on the relation between the exchange constant and the pair-correlation function of spinless electrons. This relation is valid in several independent asymptotic regimes, including low electron density case, under the general condition of a strong spin-charge separation. Explicit formulas for the exchange constant are obtained for thin quantum rings and wires with realistic Coulomb interactions by calculating the pair-correlation function via a many-body instanton approach. A remarkably smooth interpolation between high and low electron density results is shown to be possible. These results are applicable to the case of one-dimensional wires of intermediate width as well. Our method can be easily generalized to other interaction laws, such as the inverse distance squared one of the Calogero-Sutherland-Moser model. We demonstrate excellent agreement with the known exact results for the latter model and show that they are relevant for a realistic experimental setup in which the bare Coulomb interaction is screened by an edge of a two-dimensional electron gas.Comment: 12 pages, 5 figure

Spin and Charge Luttinger-Liquid Parameters of the One-Dimensional Electron Gas

Low-energy properties of the homogeneous electron gas in one dimension are completely described by the group velocities of its charge (plasmon) and spin collective excitations. Because of the long range of the electron-electron interaction, the plasmon velocity is dominated by an electrostatic contribution and can be estimated accurately. In this Letter we report on Quantum Monte Carlo simulations which demonstrate that the spin velocity is substantially decreased by interactions in semiconductor quantum wire realizations of the one-dimensional electron liquid.Comment: 13 pages, figures include

Effective charge-spin models for quantum dots

It is shown that at low densities, quantum dots with few electrons may be mapped onto effective charge-spin models for the low-energy eigenstates. This is justified by defining a lattice model based on a many-electron pocket-state basis in which electrons are localised near their classical ground-state positions. The equivalence to a single-band Hubbard model is then established leading to a charge-spin ($t-J-V$) model which for most geometries reduces to a spin (Heisenberg) model. The method is refined to include processes which involve cyclic rotations of a ``ring'' of neighboring electrons. This is achieved by introducing intermediate lattice points and the importance of ring processes relative to pair-exchange processes is investigated using high-order degenerate perturbation theory and the WKB approximation. The energy spectra are computed from the effective models for specific cases and compared with exact results and other approximation methods.Comment: RevTex, 24 pages, 7 figures submitted as compressed and PostScript file