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Q 44 Gruppenberichte Quantengase
Zeit: Donnerstag 16:30–18:30 Raum: HS 225
Gruppenbericht Q 44.1 Do 16:30 HS 225
Realization of an Atom Laser based on Bose-Einstein condensates
in magneti field insensitive states — •Giovanni Cennini,
Gunnar Ritt, Carsten Geckeler, and Martin Weitz —
Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle
14, 72076 Tübingen Germany.
A novel type of atom laser is realized by all optical techniques [1]. Our
experiment is based on a Bose-Einstein condensate (BEC) of atoms generated
by direct evaporative cooling of atoms in a single beam optical
dipole trap. The atoms are in mF = 0 Zeeman state, making this atom
laser insensitive to stray magnetic fields.
In our apparatus, cold rubidium atoms are initially prepared in a
magneto-optical trap and then transferred to a CO2-laser optical dipole
trap. Such optical traps offer a state-independent confinement, allowing
for studies of atomic systems which cannot be stored in magnetic traps,
such as multiple spin-states. Evaporation to a BEC is achieved by continuously
lowering the trapping potential depth. This generates a spinor
condensate with 1.2 ×10 4 atoms distributed among the different Zeeman
states of the hyperfine ground state F = 1. When a moderate magnetic
gradient is applied, the atoms condense into a field insensitive mF = 0
Zeeman state alone. Once the degenerate regime is achieved, the trapping
potential is smoothly lowered until gravity couples out condensed atoms.
The stability of the generated coherent, monoenergetic beam is limited
only by trapping laser intensity fluctuations.
Gruppenbericht Q 44.2 Do 17:00 HS 225
Coherent matter waves near surfaces — •Peter Krüger 1 ,
Stephan Wildermuth 1 , Sebastian Hofferberth 1 , Mauritz
Andersson 1 , Sönke Groth 1,2 , Elmar Haller 1 , Leonardo
Della Pietra 1 , Mihael Brajdic 1 , Israel Bar-Joseph 2 , and
Jörg Schmiedmayer 1 — 1 Physikalisches Institut, Universität
Heidelberg, 69120 Heidelberg — 2 Weizmann Institut, Rehovot, Israel
Surface mounted current and charge carrying structures can be used
to tailor a great variety of different micro-potentials for neutral atoms. In
analogy to electronic chips, atom chips for the controlled manipulation
of matter waves can be formed. At this stage, a number of atom-optical
tools, such as traps, guides, and beam splitters have been developed and
tested in the laboratory, and experiments in different fields of physics
have become possible.
Here, we report on our investigations with Bose-Einstein condensates
(BEC) and ultracold thermal atoms just above the critical condensation
temperature. Surface disorder potentials are studied with atoms that are
separated from a conductor surface by tens of microns down to a few
microns. We will present results for stationary traps as well as matter
wave guides in which the atoms are transported in a controlled way.
The extreme sensitivity of dilute BECs to any potential roughness allows
to characterize the surface potential with high precision. From our
Q 45 Quanteninformation IV
experiments, the high demands on the chip fabrication become apparent
and the possibilities for coherent manipulation of matter waves can be
judged. This is of particular relevance for the implementation of elementary
quantum processors on atom chips.
Gruppenbericht Q 44.3 Do 17:30 HS 225
Physik mit Spinor Bose-Einstein Kondensaten — •Holger
Schmaljohann, Michael Erhard, Jochen Kronjäger, Christoph
Becker, Thomas Garl, Kai Bongs und Klaus Sengstock
— Institut für Laserphysik, Universität Hamburg, Luruper Chaussee
149, 22761 Hamburg, Germany
Durch die geringe kinetische Energie werden in ultrakalten Quantengasen
- speziell in Bose-Einstein Kondensaten - Spindynamik, d.h. magnetische
Effekte, sichtbar. Damit werden erstmals Vergleiche allgemeiner magnetischer
Wechselwirkungen von Festkörpersystemen bis hin zu Gasen
möglich. Wir geben einen Überblick über unsere aktuellen experimentellen
und theoretischen Ergebnisse zu den statischen und dynamischen
magnetischen Eigenschaften von 87 Rb Bose-Einstein Kondensaten. Wir
präsentieren Messungen zum Grundzustand von 87 Rb, die in der F=1
Hyperfein-Mannigfaltigkeit ferromagnetisches und in der F=2 Mannigfaltigkeit
antiferromagnetisches Verhalten zeigen [1]. Zudem diskutieren
wir das reichhaltige Wechselspiel zwischen kohärenter Dynamik und inkohärenter
Spindynamik durch Thermalisierungseffekte.
[1] H. Schmaljohann et al., cond-mat/0305497.
Gruppenbericht Q 44.4 Do 18:00 HS 225
Low dimensional Bose gases in optical lattices — •Michael
Köhl, Thilo Stöferle, Henning Moritz, Christian Schori, and
Tilman Esslinger — Institut für Quantenelektronik, ETH Zürich, CH-
8093 Zürich
We report on the realization and investigation of one-dimensional
trapped Bose gases in the mean-field and in the strongly interacting
regime. In the weakly interacting mean-field regime we have characterized
the gas by measuring collective excitations and we find the ratio
of the frequencies of the lowest compressional (breathing) mode and
the dipole mode to be (ωB/ωD) 2 � 3.1. For a thermal gas we measure
(ωB/ωD) 2 � 4 [1]. By adding a periodic potential along the axis of the
1D gas we can tune the gas from a strongly interacting superfluid into
the Mott-insulating phase. We study the gas by Bragg spectroscopy and
find that the excitation spectra cannot be understood by Bogoliubov
theory [2]. The excitation spectra of both phases are compared to the
three-dimensional gas and to the crossover regime from one to three dimensions.
The coherence properties of the gas in all configurations are
measured quantitatively.
[1] H. Moritz et al., to appear in Phys. Rev. Lett.
[2] T. Stöferle et al., preprint 2003.
Zeit: Freitag 11:00–13:00 Raum: HS 101
Gruppenbericht Q 45.1 Fr 11:00 HS 101
Entanglement of a single photon with an atom-cavity system —
•T. Legero, T. Wilk, M. Hennrich, A. Kuhn, and G. Rempe —
Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748
Garching, Germany
The coalescence of two identical photons superposed on a 50/50 beamsplitter
is a well known effect [1], for which a time resolved analysis reveals
that it can also be interpreted as a measurement induced entanglement,
followed by an interferometric verification. Because the beamsplitter conceals
the origin of the first detected photon, the remaining photon is projected
into a path-entangled state [2]. We apply this effect to entangle a
single atom with a single photon, and to determine degree and lifetime
of the entanglement.
A strongly coupled atom-cavity system generates two successive singlephoton
wave packets which are long compared to the time resolution of
our detectors [3]. The first photon is sent into a 1100 m long optical fiber
and impinges on a beamsplitter simultaneously with the second photon
that travels along a negligibly short path. Since the coherence time ex-
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ceeds the photon transit time from the source to the beamsplitter, the
first photodetection induces an entanglement between the photonic field
mode of the fiber and the state of the source atom. This entanglement is
verified in a correlation experiment where the phase of the superposition
state is changed in a controlled manner.
[1] Hong et al.PRL 59, 2044 (1987); Santori et al.Nature 419, 594 (2002)
[2] Legero et al.Appl.Phys.B77, 797 (2003)
[3] Kuhn et al.PRL 89, 67901 (2002)
Q 45.2 Fr 11:30 HS 101
Quantum dot single photon sources: prospects for applications
in linear optics quantum computation — •Alper Kiraz 1 , Mete
Atatüre 2 , and Atac Imamo¯glu 2 — 1 Department Chemie, Ludwig-
Maximilians Universität München, Butenandtstr. 11, D-81377 München,
Germany — 2 Quantenelektronik, ETH-Hönggerberg, HPT G12, CH-8093
Zurich, Switzerland
An optical source that produces single photon pulses on demand has
potential applications in linear optics quantum computation, provided