aktualisiertes pdf - DPG-Tagungen

schen Feldern, die von mikrostrukturierten Leiterbahnen erzeugt werden.
Wir haben Mikrofallen entwickelt, bei denen das magnetische Fallenpotential
durch elektrostatische Felder auf der Mikrometerskala strukturiert
wird. Die Berechnung und Herstellung dieser Fallen sowie aktuelle Experimente
werden vorgestellt.
Q 21.8 Di 14:00 Schellingstr. 3
Beyond Gutzwiller: Corrections to mean-field expansion
patterns of interacting bosonic atoms in optical lattices. —
•Christian Schroll 1 , Florian Marquardt 2 , and Christoph
Bruder 1 — 1 Universität Basel, Departement für Physik und
Astronomie, Klingelbergstr. 82, CH-4056 Basel, Schweiz — 2 Yale
University, Dept. of Physics, New Haven, USA
We consider the Mott-insulator transition in optical lattices, studying
in particular short-range correlations that determine the momentum
distribution and the experimentally observed expansion patterns. Based
on the mean-field Gutzwiller ansatz, which is a good approximation for
small and large ratio of the hopping to onsite energy J/U, we use perturbation
theory to improve the results for intermediate values of J/U. We
discuss the resulting substantial modifications of the density fluctuations
and the density matrix, and we compare to other approaches.
Q 21.9 Di 14:00 Schellingstr. 3
Precision real-time evolution of a freely falling BEC — •Gerrit
Nandi, Reinhold Walser, and Wolfgang P. Schleich —
Abteilung für Quantenphysik, Universität Ulm, Germany
Free falling Bose-Einstein condensates (BEC) that are only subject to
micro-gravity provide a new experimental setup to study the non-classical
nature of a condensed quantum system. The long-time unconstraint expansion
of an ultra-cold Bose gas magnifies sub-healing length physics
and allows for a measurement of the macroscopic wave function and its
higher correlations [1]. Exact symmetries of the system such as the generalized
harmonic potential theorem [2] or the breathing mode [3] can be
studied in un-precedented detail.
The detailed description of the freely falling condensate depends on the
particular launch procedure and geometry. This requires the numerical
solution of the coupled Gross-Pitaevskii equation for the semi-classical
field amplitude, the background density and the pair correlation function
in real time[4].
[1] D. Helleweg, L. Cacciapuoti, M. Kottke, T. Schulte, K. Sengstock,
W. Ertmer, and J. Arlt, Phys. Rev. Lett. 91, 010406 (2003)
[2] J. Dobson Phys. Rev. Lett. 73, 2244-2247 (1994)
[3] L.Pitaevskii and A. Rosch Phys. Rev. A 55 , R853-R856 (1997)
[4] R.Walser, J. Cooper, and M. Holland, Phys. Rev. A 63, 13607 (2001)
Q 21.10 Di 14:00 Schellingstr. 3
Light propagation in Gödel’s universe — •Endre Kajari, Reinhold
Walser, and Wolfgang P. Schleich — Abteilung für Quantenphysik,
Universität Ulm, Germany
The physics of cold quantum gases has many common themes with
other important fields of physics, such as solid state physics, condensed
matter physics and also general relativity e.g. [1]. In the present contribution,
we are interested in a perculiar modell of curved spacetime,
which was introduced by Kurt Gödel in 1949 [2]. This cosmological solution
of Einstein’s field equations possesses closed timelike curves, due to
its strange causal structure. In here we will examine the light propagation
in this universe. First we will investigate the geometric optical limit. In a
second step we will solve Maxwell’s equation in vacuum in an alternative
approach to M. Cohen [3]. In particular we will discuss the influence of
the causal structure to the proper formulation of a Cauchy initial value
formulation.
[1] G.E.Volovik, The Universe in a Helium Droplet, Oxford Univ Pr
(2003)
[2] K. Gödel, Rev. Mod. Phys. 21, 447 (1949)
[3] M. Cohen, C. V. Vishveshwara, S. V. Dhurandhar, J. Phys. A 13, 933
(1980)
Q 21.11 Di 14:00 Schellingstr. 3
Wechselwirkung von ultrakalten Rubidium und Cäsium Gasen
— •Michael Haas, Daniel Frese, Vanessa Leung, Arno Rauschenbeutel
und Dieter Meschede — Institut für angewandte Physik,
Rheinische Friedrich-Wilhelm Universität Bonn
In der letzten Zeit ist das Interesse an kalten Gasgemischen und hete-
100
ronuklearen Molekülen gestiegen. In diesem Zusammenhang ist es insbesondere
der Gruppe von deMille gelungen [1], mittels Photoassoziation
ultrakalte RbCs Moleküle zu erzeugen. Das Bonner BEC Experiment
ist auf die Untersuchung der Wechselwirkung von ultrakalten Rubidium
und Cäsium Atomen, sowie insbesondere für die Erforschung weniger
Cäsiumatome in einem Rubdiumkondensat ausgelegt. Wir berichten in
diesem Poster über den Stand des Experiments.
[1] deMille et al. ”Production of ultracold, polar RbCs* molecules via
photoassociation”, bei PRL zur Veröffentlichung akzeptiert
Q 21.12 Di 14:00 Schellingstr. 3
Bose-Einstein condensation in a single-beam dipole trap and
an all-optical atom laser — Giovanni Cennini, •Carsten Geckeler,
Gunnar Ritt, and Martin Weitz — Physikalisches Institut,
Tübingen, Germany
We have created a Bose-Einstein condensate (BEC) by direct evaporative
cooling of 87 Rb atoms in a quasistatic optical dipole trap formed by
a focused single running CO2-laser beam with wavelength near 10.6µm.
About 4 × 10 6 atoms are loaded from a magneto-optical trap into the
dipole trap. Forced evaporative cooling is achieved by continously lowering
the trap depth, and generates a F = 1 spinor condensate with
12000 atoms. The phase transition occurs at a temperature of 180nK.
Further, we have realized a BEC in the mF = 0 spin projection by applying
a moderate magnetic field gradient during evaporation. With this
field gradient activated, typically 7000 atoms condense into the mF = 0
component alone. The chemical potential of the realized condensate is
first order insensitive to magnetic field fluctuations. Finally, a collimated
and monoenergetic beam of atoms can be extracted from the BEC by
smoothly lowering the dipole trapping potential to form an all-optical
atom laser.
Q 21.13 Di 14:00 Schellingstr. 3
Kollektive Anregungen in quasi-eindimensionalen Quantengasen
— •Markus Kottke, Thomas Schulte, Sascha Drenkelforth,
Wolfgang Ertmer und Jan Arlt — Institut für Quantenoptik;
Universität Hannover; Welfengarten 1; 30167 Hannover
Die Eigenschaften niederdimensionaler Systeme sind in einer Vielzahl
physikalischer Fragestellungen von zentralem Interesse. Seit kurzem ist
es möglich, solche Systeme in besonders reiner Form mit ultrakalten,
quantenentarteten atomaren Gasen zu verwirklichen. Signaturen solch
niederdimensionaler Systeme sind z.B. ihre Anregungsfrequenzen oder
ihre Kohärenzeigenschaften.
Wir haben den Anregungszustand der niedrigen m=0 quadrupol
Oszillation in stark elongierten bzw. eindimensionalen Bose-Einstein-
Kondensaten untersucht und im Vergleich mit theoretischen Untersuchungen
vermessen. Insbesondere der Einfluss der thermischen Wolke in
der Falle muss jedoch für diese Messungen berücksichtigt werden, da er
die Oszillationsfrequenz auf einer vergleichbaren Größenskala verschiebt.
Wir haben die Frequenzverschiebung zwischen dem 3D-Mean-Field und
1D-Mean-Field Regime vermessen und finden gute Übereinstimmung mit
den theoretischen Vorhersagen.
Q 21.14 Di 14:00 Schellingstr. 3
Macroscopic quantum self trapping — •Stefan Hunsmann,
Thomas Anker, Michael Albiez, Bernd Eiermann, Rudolf
Gati, and Markus K. Oberthaler — Kirchhoff-Institut für Physik,
Universität Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg
The nonlinear matter wave dynamics in periodic potentials opens up
a very rich field of physics. For small nonlinearity, corresponding to low
atomic densities, and weak periodic potentials we realized non-spreading
wave packets - atomic gap solitons[1].
In this poster we discuss the regime with moderate atomic densities and
deep periodic potentials. Here the dynamics is conveniently described by
looking at the atomic tunnelling current from well to well. The tunnelling
dynamics is similar to that of a Josephson-junction, where atom-atom interaction
enriches the possible tunnelling modes. The most prominent effect
is the possibility that a sufficiently big density difference between two
wells can prevent further tunnelling and thus halts the wave packet dynamics
- an effect called ”macroscopic quantum self trapping”(MQST)[2].
We present first experimental results on MQST realized with 87 Rb
Bose-Einstein condensates in a quasi 1D wave guide.
[1] see talk ”Helle Gap-Solitonen für Atome mit repulsiver Wechselwirkung”.
[2] A. Trombettoni and A. Smerzi, Phys. Rev. Lett. 86, 2353 (2001).