The Bonn University lidar at the Esrange: technical description and capabilities for atmospheric research

International audienceThe Bonn University operates a Rayleigh/Mie/Raman backscatter lidar at the Esrange near the Swedish city of Kiruna, north of the Arctic circle. The lidar system covers the atmosphere from about 4 km to 100 km altitude and it is capable of measuring aerosols in the tropo-, strato-, and mesosphere, as well as of determining temperature profiles in the aerosol-free part of the atmosphere (i.e. above 30-km altitude). Density tuned fixed-spacer etalons provide daylight capability and thus increased sensitivity to noctilucent clouds during polar summer. Polarisation measurements allow liquid and solid phase discrimination for aerosol and cloud particles in the tropo- and stratosphere. The derived temperature profiles can be used for the detection and analysis of atmospheric gravity waves. Although several lidar experiments are situated in polar latitudes, a comprehensive instrument which covers the troposphere, stratosphere, and mesosphere, is daylight capable, and observes temperature profiles, as well as aerosols, is exceptional. In this article a technical description, in particular, of the optical configuration of this experiment is given, as well as an overview of achievable geophysical parameters. The potential for geophysical analyses is shown. Keywords. Atmospheric composition and structure (Instruments and techniques; Aerosols and particles; Pressure, density and temperature) ? Meteorology and atmospheric dynamics (Middle atmosphere dynamics

Optimized design of universal two-qubit gates

We construct optimized implementations of the CNOT and other universal two-qubit gates that, unlike many of the previously proposed protocols, are carried out in a single step. The new protocols require tunable inter-qubit couplings but, in return, show a significant improvements in the quality of gate operations. Our optimization procedure can be further extended to the combinations of elementary two-qubit as well as irreducible many-qubit gates.Comment: 6 pages, 2 figure

Simultaneous lidar observations of temperatures and waves in the polar middle atmosphere on the east and west side of the Scandinavian mountains: a case study on 19/20 January 2003

Atmospheric gravity waves have been the subject of intense research for several decades because of their extensive effects on the atmospheric circulation and the temperature structure. The U.&nbsp;Bonn&nbsp;lidar at the Esrange and the ALOMAR RMR lidar at the And&#248;ya Rocket Range are located in northern Scandinavia 250 km apart on the east and west side of the Scandinavian mountain ridge. During January and February&nbsp;2003 both lidar systems conducted measurements and retrieved atmospheric temperatures. On 19/20 January&nbsp;2003 simultaneous measurements for more than 7 h were possible. Although during most of the campaign time the atmosphere was not transparent for the propagation of orographically induced gravity waves, they were nevertheless observed at both lidar stations with considerable amplitudes during these simultaneous measurements. And while the source of the observed waves cannot be determined unambiguously, the observations show many characteristics of orographically excited gravity waves. The wave patterns at ALOMAR show a random distribution with time whereas at the Esrange a persistency in the wave patterns is observable. This persistency can also be found in the distribution of the most powerful vertical wavelengths. The mode values are both at about 5 km vertical wavelength, however the distributions are quite different, narrow at the Esrange with values from &lambda;<i>_z</i>=2&ndash;6 km and broad at ALOMAR, covering &lambda;<i>_z</i>=1&ndash;12 km vertical wavelength. In particular the difference between the observations at ALOMAR and at the Esrange can be understood by different orographic conditions while the propagation conditions were quite similar. At both stations the waves deposit energy in the atmosphere with increasing altitude, which leads to a decrease of the observed gravity wave potential energy density with altitude. The meteorological situation during these measurements was different from common winter situations. The ground winds were mostly northerlies, changed in the upper troposphere and lower stratosphere to westerlies and returned to northerlies in the middle stratosphere

Simultaneous lidar observations of temperatures and waves in the polar middle atmosphere on both sides of the Scandinavian mountains: a case study on 19/20 January 2003

International audienceAtmospheric gravity waves have been the subject of intense research for several decades because of their extensive effects on the atmospheric circulation and the temperature structure. The U. Bonn lidar at the Esrange and the ALOMAR RMR lidar at the Andøya Rocket Range are located in northern Scandinavia 250 km apart on either side of the Scandinavian mountain ridge. During January and February 2003 both lidar systems conducted measurements and retrieved atmospheric temperatures. On 19/20 January 2003 simultaneous measurements for more than 7 h were possible. Although during most of the campaign time the atmosphere was not transparent for the propagation of orographically induced gravity waves, they could propagate and were observed at both lidar stations during these simultaneous measurements. The wave patterns at ALOMAR show a random distribution with time whereas at the Esrange a persistency in the wave patterns is observable. This persistency can also be found in the distribution of the most powerful vertical wavelengths. The mode values are both at about 5 km vertical wavelength, however the distributions are quite different, narrow at the Esrange containing values from ?z=2?6 km and broad at ALOMAR, covering ?z=1?12 km vertical wavelength. At both stations the waves deposit energy in the atmosphere with increasing altitude, which leads to a decrease of the observed gravity wave potential energy density with altitude. These measurements show unambigiously orographically induced gravity waves on both sides of the mountains as well as a clear difference of the characteristics of these waves, which might be caused by different excitation and propagation conditions on either side of the Scandinavian mountain ridge

A many-fermion generalization of the Caldeira-Leggett model

We analyze a model system of fermions in a harmonic oscillator potential under the influence of a dissipative environment: The fermions are subject to a fluctuating force deriving from a bath of harmonic oscillators. This represents an extension of the well-known Caldeira-Leggett model to the case of many fermions. Using the method of bosonization, we calculate one- and two-particle Green's functions of the fermions. We discuss the relaxation of a single extra particle added above the Fermi sea, considering also dephasing of a particle added in a coherent superposition of states. The consequences of the separation of center-of-mass and relative motion, the Pauli principle, and the bath-induced effective interaction are discussed. Finally, we extend our analysis to a more generic coupling between system and bath, that results in complete thermalization of the system.Comment: v3: fixed pdf problem; v2: added exact formula (Eq. 42) for Green's function and discussion of equilibrium density matrix (new Fig. 2); 10 figures, 21 pages, see quant-ph/0305098 for brief version of some of these result

Heralded processes on continuous-variable spaces as quantum maps

Conditional evolution is crucial for generating non-Gaussian resources for quantum information tasks in the continuous variable scenario. However, tools are lacking for a convenient representation of heralded process in terms of quantum maps for continuous variable states, in the same way as Wigner functions are able to give a compact description of the quantum state. Here we propose and study such a representation, based on the introduction of a suitable transfer function to describe the action of a quantum operation on the Wigner function. We also reconstruct the maps of two relevant examples of conditional process, that is, noiseless amplification and photon addition, by combining experimental data and a detailed physical model. This analysis allows to fully characterize the effect of experimental imperfections in their implementations.Comment: 9 pages, 8 figures. Minor change

Decoherence of a two-qubit system with a variable bath coupling operator

We examine the decoherence of an asymmetric two-qubit system that is coupled via a tunable interaction term to a common bath or two individual baths of harmonic oscillators. The dissipative dynamics are evaluated using the Bloch-Redfield formalism. It is shown that the behaviour of the decoherence effects is affected mostly by different symmetries between the qubit operator which is coupled to the environment and temperature, whereas the differences between the two bath configurations are very small. Moreover, it is elaborated that small imperfections of the qubit parameters do not lead to a drastic enhancement of the decoherence rates.Comment: 10 pages, 5 figure

Optimierung der Saatgutgesundheit im ökologischen Arznei- und Gewürzpflanzenanbau

In dem BÖL Vorhaben „Optimierung der Saatgutqualität im ökologischen Arznei- und Gewürzpflanzenanbau“ Projekt 03OE127/1 (Laufzeit: 01.04.2004 – 31.12.2006) wurden schwerpunktmäßig Versuche zur Saatgutbehandlung durchgeführt. Für die Modellkulturen Anis, Dill, Fenchel, Koriander und Kümmel aus der Familie der Umbelliferae wurden Kenngrößen zum Einsatz von Pflanzenstärkungsmitteln zur Saatgutbehandlung erarbeitet und verschiedene physikalische Behandlungsmaßnahmen geprüft. Im Ergebnis dreier Jahre konnte kein durchgehend positiver Einfluss eines Pflanzenstärkungsmittels auf die Keimfähigkeit und den Feldaufgang ermittelt werden. Die physikalischen Behandlungsmaßnahmen (Heißwasserbehandlung, Elektronenbehandlung) zeigten in einzelne Pathosystemen sehr gute Wirksamkeiten. Ein kritischer Punkt dieser Behandlungen ist allerdings das Risiko eines Keimfähigkeitsverlustes. Die Versuchsarbeiten verdeutlichten, dass die Parameter der physikalischen Saatgutbehandlungen sehr genau auf die jeweils einzelne Saatgutpartie abgestimmt werden muß, um neben hohen Wirkungsgraden die Keimfähigkeit zu erhalten. Die Vakuum-Sattdampfbehandlung wurde als neueres Verfahren im Modell geprüft und erbrachte an Petersiliensaatgut eine Reduktion von Alternaria radicina. Ein weiterer Teilbereich des Projektes beschäftigte sich mit dem Einfluss pflanzenbaulichen Maßnahmen auf die Saatgutqualität. Im Besonderen wurde durch eine Variation des Erntezeitpunktes bei einigen Arten eine erhöhte Keimfähigkeit sowie unterschiedliche Befallsgrade von samenbürtigen Pathogen ermittelt. Neben den umfangreichen Arbeiten zur Saatgutqualität wurden die Saatgutpillierung von Petersilie und Kümmel untersucht. Die Schwierigkeit des Vorhabens lag im fehlenden Grundlagenwissen zu vielen Wirt-Pathogenbeziehungen. Resultierend aus den Versuchsarbeiten können der Praxis umfangreiche Erfahrungen zur Saatgutbehandlung vorgestellt werden. Die Arbeiten verdeutlichten, dass dem Produktionsfaktor Saatgut mehr Aufmerksamkeit geschenkt werden sollte und vor dem Anbau wichtige Qualitätsparameter (Keimfähigkeit, Befall mit samenbürtigen Pathogenen) beim Saatguthandel erfragt werden sollte

Quantum nondemolition-like, fast measurement scheme for a superconducting qubit

We present a measurement protocol for a flux qubit coupled to a dc-Superconducting QUantum Interference Device (SQUID), representative of any two-state system with a controllable coupling to an harmonic oscillator quadrature, which consists of two steps. First, the qubit state is imprinted onto the SQUID via a very short and strong interaction. We show that at the end of this step the qubit dephases completely, although the perturbation of the measured qubit observable during this step is weak. In the second step, information about the qubit is extracted by measuring the SQUID. This step can have arbitrarily long duration, since it no longer induces qubit errors.Comment: published version, minor correction