A bright, pulsed two-mode squeezer

We report the realization of a bright ultrafast two-mode squeezer based on type II parametric downconversion (PDC) in periodically poled $\mathrm{KTiOPO_4}$ (PP-KTP) waveguides. It produces a pulsed two-mode squeezed vacuum state: a photon-number entangled pair of truly single-mode pulses or, in terms of continuous variables quantum optics, a pulsed, single mode Einstein-Podolsky-Rosen (EPR) state in the telecom regime. We prove the single mode character of our source by measuring its $g^{(2)}$ correlation function and demonstrate a mean photon number of up to 2.5 per pulse, equivalent to 11dB of two-mode squeezing.Comment: 4 pages, 3 figure

Detektion und Analyse physiologischer und biokinematischer Parameter mit Körpersensoren

Christ P. Detektion und Analyse physiologischer und biokinematischer Parameter mit Körpersensoren. Bielefeld: Universität Bielefeld; 2016

Towards a perfect fixed point action for SU(3) gauge theory

We present an overview of the construction and testing of actions for SU(3) gauge theory which are approximate fixed points of renormalization group equations (at $\beta\rightarrow \infty$). Such actions are candidates for use in numerical simulations on coarse lattices.Comment: 6 pages, uuencoded compressed postscript file, contribution to LAT9

First Blood Vessels in the Avian Neural Tube Are Formed by a Combination of Dorsal Angioblast Immigration and Ventral Sprouting of Endothelial Cells

AbstractWe studied the early pattern of neural tube (NT) vascularization in quail embryos and chick–quail chimeras. Angioblasts appeared first in the dorsal third at Hamburger and Hamilton (HH) stage 19 as single, migrating cells. Their distribution did not correspond to a segmental pattern. After this initial dorsal immigration, endothelial sprouts invaded the NT on either side of the floor plate (HH stage 21). These cells remained continuous with their arterial vascular sources, connected to the venous perineural vascular plexus at HH-stage 22, and formed the first perfused vessels of the NT at HH-stage 23. The same pattern of angiotrophic vascularization was observed in a craniocaudal sequence starting caudal to the rhombencephalic NT. Extremely long filopodia were observed on sprouting cells, extending toward the central canal and the mantle layer. The exclusively extraneuroectodermal origin of angioblastic cells was demonstrated with chick–quail chimeras. Following replacement of quail NT by chick NT graft, angioblast and sprout distribution in chimeras was the same as in controls. We conclude that the NT receives its first blood vessels by a combination of two different processes, dorsal immigration of isolated migrating angioblastic cells and ventral sprouting of endothelial cells, which derive from perfused vessels. The dorsal invasive angioblasts contribute to the developing intraneural vascular plexus after having traversed the neural tube. The initial distribution of blood vessels within the neuroepithelium corresponds to intrinsic random motility of angioblastic cells; a more regular pattern is seen later. The floor plate apparently prohibits connections between sprouts in both NT sides, whereas in the dorsal NT, such a separating effect on the migrating angioblasts does not exist

Direct Measurement of the Spatial-Spectral Structure of Waveguided Parametric Down-Conversion

We present a study of the propagation of higher-order spatial modes in a waveguided parametric down-conversion photon pair source. Observing the multimode photon pair spectrum from a periodically poled KTiOPO$_4$ waveguide allowed us to isolate individual spatial modes through their distinctive spectral properties. We have measured directly the spatial distribution of each mode of the photon pairs, confirming the findings of our waveguide model, and demonstrated by coincidence measurements that the total parity of the modes is conserved in the nonlinear interaction. Furthermore, we show that we can combine the advantages of a waveguide source with the potential to generate spatially entangled photon pairs as in bulk crystal down-converters.Comment: 4 pages, 5 figure

SU(2) Yang-Mills quantum mechanics of spatially constant fields

As a first step towards a strong coupling expansion of Yang-Mills theory, the SU(2) Yang-Mills quantum mechanics of spatially constant gauge fields is investigated in the symmetric gauge, with the six physical fields represented in terms of a positive definite symmetric (3 x 3) matrix S. Representing the eigenvalues of S in terms of elementary symmetric polynomials, the eigenstates of the corresponding harmonic oscillator problem can be calculated analytically and used as orthonormal basis of trial states for a variational calculation of the Yang-Mills quantum mechanics. In this way high precision results are obtained in a very effective way for the lowest eigenstates in the spin-0 sector as well as for higher spin. Furthermore I find, that practically all excitation energy of the eigenstates, independently of whether it is a vibrational or a rotational excitation, leads to an increase of the expectation value of the largest eigenvalue , whereas the expectation values of the other two eigenvalues, and , and also the component = g of the magnetic field, remain at their vacuum values.Comment: 7 pages, 4 figure

Gigabit Produktionsnetze in der HWW

Unter der Bezeichnung HLRS (Höchstleistungsrechenzentrum Stuttgart) ist am RUS das erste Supercomputerzentrum für den universitären Wissenschaftsbereich in der Bundesrepublik angesiedelt. Derzeit plant die DFG zwei bis drei solcher Zentren. Das inzwischen realisierte Breitband-Wissenschaftsnetz (BWiN) garantiert dabei eine effektive Erreichbarkeit solcher Zentren. Unter der Bezeichnung HWW (Höchstleistungsrechner für Wissenschaft und Wirtschaft) haben Land und Universität zusammen mit den Firmen debis Systemhaus und Porsche AG eine gemeinsame Betriebsgesellschaft gegründet. Diese betreibt auch die im Rahmen des HLRS beschafften Rechner. Die HWW wird ein zwischen dem RUS-Standort Campus Vaihingen und dem debis-Sitz Untertürkheim verteiltes Rechenzentrum etablieren und betreiben. Vom RUS wurde in diesem Kontext am 15. August die Abnahme der NEC SX-4/32 (s. BI 7/8 1996) erfolgreich abgeschlossen; die Maschine wurde anschließend der HWW zum Betrieb übergeben. Die nächste Maschine wird entsprechend eine Cray T-3E/512 sein - aufgestellt am debis-Standort. Dort stehen bereits eine Cray T93 und eine Cray J90, die ebenfalls von der HWW betrieben werden. Der vorliegende Artikel beschreibt in diesem Zusammenhang das HWW-Netz mit besonderer Berücksichtigung der schnellen Verbindung Vaihingen-Untertürkheim. In einem weiteren Artikel, HWW-Link - Optik und SDH, wird zudem die Problematik des physikalischen Bit-Transporteszwischen den HWW-Standorten behandelt

Was gibt's Neues im BelWü?

Seit Anfang April des Jahres sind an den Universitäten Freiburg, Heidelberg, Karlsruhe, Mannheim und Stuttgart jeweils 34 MBit/s Breitband-Wissenschaftsnetz-Anschlüße (BWiN) im Einsatz - an den restlichen Universitäten, Hohenheim, Konstanz, Tübingen und Ulm, seit Ende April. Diese Hochgeschwindigkeitszugänge werden von der Telekom im Auftrag des DFN auf ATM-Basis zur Verfügung gestellt. Vom DFN-NOC an der Universität Stuttgart wird hierüber der IP-Dienst realisiert. Die bisherigen 2 bzw. 34 MBit/s BelWü-Datex-M-Anschlüße werden zum 01. Juli 1996 abgeschaltet werden

Temperature dependence of the electrical conductivity of imidazolium ionic liquids.

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10^7 Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion.ionic liquids; molten salts;