aktualisiertes pdf - DPG-Tagungen

Q 40.8 Do 18:15 HS 204
Investigation of photosynthetic processes by picosecond fluorescence
spectroscopy — •Franz-Josef Schmitt 1 , Hans Joachim
Eichler 1 , Hann-Jörg Eckert 2 , and Joachim Huyer 1 — 1 Optisches
Institut - P 1-1, Technische Universität Berlin, Strasse des 17. Juni 135,
D-10623 Berlin — 2 Max-Volmer-Laboratorium, Technische Universität
Berlin, Strasse des 17. Juni 135, D-10623 Berlin
The primary processes of photosynthesis in higher plants and
Cyanobacteria start with the generation of excited states by light absorption
within pigment-protein complexes forming the antenna system
(mainly Chlorophyll molecules). The electronic excitation then migrates
via singlet-singlet energy transfer to the reaction center where it induces
Q 41 Quanteneffekte III
a primary charge separation leading to a primary radical pair (P+A-
). Information on these processes can be gathered from analyses of the
dynamics and wavelength dependence of the emitted fluorescence. Both
can be obtained in short acquisition times by using a novel single photon
counting fluorometer system which permits to monitor simultaneously
the time and wavelength dependence of the fluorescence emission. The
key element of this equipment is a special microchannel-plate photomultiplier
with delay-line anode. The data are recorded by a two-dimensional
multi-channel-analyzer on the basis of a computer system. In this report
we compare the time resolved fluorescence spectra of various photosynthetic
organisms with different Chlororophyll types (Chl a, Chl b, Chl d)
in the antenna system.
Zeit: Donnerstag 16:30–18:30 Raum: HS 218
Gruppenbericht Q 41.1 Do 16:30 HS 218
Dynamical theory of Casimir-Polder forces on excited atoms
— •Stefan Yoshi Buhmann 1 , Ho Trung Dung 1,2 , Dirk-Gunnar
Welsch 1 , and Ludwig Knöll 1 — 1 Theoretisch-Physikalisches Institut,
Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena,
Germany — 2 Institute of Physics, National Center for Sciences and Technology,
1 Mac Dinh Chi Street, District 1, Ho Chi Minh city, Vietnam
Based on macroscopic quantum electrodynamics, a dynamical theory
of the Casimir-Polder force acting on an excited atomic system near
an arbitrary arrangement of dispersing and absorbing magnetodielectric
bodies is presented. It is shown that in the weak-coupling regime the
total force as a function of time is a superposition of force components
that are related to the atomic density matrix elements at chosen time.
In particular, it is found that when the atomic system is initially prepared
in a coherent superposition of energy eigenstates, then temporally
oscillating force components are observed, which is in stark contrast to
the case of incoherent state preparation. Finally, it is shown that even
the Casimir-Polder force observed after de-excitation of the atomic system
is not exactly derivable from a potential, because of the position
dependence of the atomic polarizability.
Q 41.2 Do 17:00 HS 218
Resonante Photonenerzeugung in einer Kavität durch dynamischen
Casimir-Effekt — •Michael Uhlmann, Günter Plunien
und Gerhard Soff — Institut für Theoretische Physik, Technische
Universität Dresden, Zellescher Weg 17, 01062 Dresden
Der dynamische Casimir-Effekt beschreibt die Erzeugung von Teilchen
(z.B. Photonen) aus dem Vakuum durch eine zeitabhängige Störung, z.B.
innerhalb einer Kavität mit einem sich bewegenden Spiegel.
In dieser Arbeit wird die Bewegung eines Spiegels durch eine dünne
Schicht mit zeitabhängigem Brechungsindex (ɛ oder µ) simuliert. Das
elektromagnetische Feld in der idealleitenden Kavität - beschrieben durch
die makroskopischen Maxwell-Gleichungen - wird quantisiert und die resonante
Teilchenproduktion im Rahmen der Rotating Wave Approximation
(RWA) beschrieben. Es wird auf Unterschiede zwischen den beiden
Polarisationen (TE- und TM-Moden), sowie verschiedene Dynamiken des
Mediums eingegangen. Ziel ist die Beschreibung eines geplanten Experiments.
Diese Arbeit wurde unterstützt von BMBF, GSI und DFG.
Q 41.3 Do 17:15 HS 218
Deterministic single photon pulses from an ion-cavity system
— •Matthias Keller 1 , Birgit Lange 1 , Kazuhiro Hayasaka 2 ,
Wolfgang Lange 1 , and Herbert Walther 1 — 1 Max-Planck-
Institut für Quantenoptik, Garching, Germany — 2 Communications
Research Laboratory, Kobe, Japan
A single atom in a high-finesse optical cavity is an ideal source of single
photons. Each photon is triggered by an external pump pulse and
delivered to a well-defined output mode [1,2]. Completely deterministic
output characteristics and a high cw-efficiency of the device require a
continuous and controlled interaction between atom and field. We have
met this condition by localizing a single 40 Ca + -ion in a small optical cavity.
By means of laser Doppler-cooling, the position spread of the ion’s
wavepacket along the cavity axis was reduced to 5% of the transition
wavelength, so that the Lamb-Dicke regime is reached [3].
The cavity is coupled to the transition from the excited P1/2 level to
125
the metastable state D3/2 in 40 Ca + at a wavelength of λ = 866nm. We
generate single photons by driving a cavity assisted Raman transition between
ground- and D-state. Mirrors with ultralow losses on the order of
10 ppm ensure a high outcoupling efficiency. The system has the potential
to generate other non-classical states of the electromagnetic field.
[1] C.K.Law, H.J.Kimble, J. Mod. Opt. 44, 2067 (1997).
[2] A.Kuhn, M.Hennrich, G.Rempe, Phys. Rev. Lett. 89, 67901 (2002).
[3] G.R.Guthöhrlein, M.Keller, K.Hayasaka, W.Lange, and H.Walther,
Nature 414, 49 (2001).
Q 41.4 Do 17:30 HS 218
Lebensdauer des metastabilen D5/2 Niveaus eines 40Ca + Ions bei
Ankopplung an das Vakuumfeld in einem Resonator — •Axel
Kreuter, Christoph Becher, Gavin Lancaster, Carlos Russo,
Ferdinand Schmidt-Kaler und Rainer Blatt — Institut für
Experimentalphysik, Universität Innsbruck, Austria
Die natürliche Lebensdauer des D5/2 Niveaus von 40Ca + wurde an einem
einzelnen gefangenen Ion mithilfe einer wechselwirkungsfreien Methode
gemessen. Anders als bei der Quantensprung-Methode wird das Ion
nicht kontinuierlich beobachtet, sondern der Zerfall nach einer wechselwirkungsfreien
Wartezeit gemessen. Das Ergebnis τ=1160(14)ms stimmt
innerhalb einer Standardabweichung mit dem genauesten veröffentlichten
Wert überein. Diese Methode wurde dazu verwendet, die Verkürzung
der Lebensdauer zu messen, die aus der Ankopplung des Ions an das
Vakuumfeld in einem Resonator resultiert. Der Resonator wurde dafür
mithilfe eines Transfer-Lasers auf den S1/2-D5/2 Übergang stabilisiert.
Dieses Experiment zeigt, dass die kontrollierte Kopplung von Atom und
(Vakuum)Resonatorfeld über längere Zeit möglich ist. Das ist die Voraussetzung
für die Realisierung einer Reihe von Vorschlägen zur Quanteninformationsverarbeitung
mit Ionen in optischen Resonatoren.
Q 41.5 Do 17:45 HS 218
Single atom capturing effect from a single distant mirror —
•Alex Wilson, Pavel Bushev, Jürgen Eschner, and Rainer
Blatt — Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße
25, A-6020 Innsbruck, Austria
A single, trapped barium ion is seen to experience vacuum field forces
due to the presence of a single, plane, mirror some 25 cm away. These
forces are associated with a mirror-induced shift of the excited state,
which was recently observed using a spectroscopic method to probe the
internal state of the ion [1]. This shift is the dispersive counterpart to the
modified spontaneous decay rate previously observed [2]. The magnitude
of these effects are scaled by the collection efficiency of the lens that collimates
light from the 138 Ba + ion onto the retro-reflecting mirror. Scanning
the ion-mirror distance leads to a sinusoidally-varying shift of the excited
state. The mirror therefore establishes weak trapping and anti-trapping
potentials that alter the strong confining potential of the Paul trap. A
new technique has enabled the sensitive and rapid measurement of the
ion’s 1 MHz oscillation frequency. This trap frequency is seen to vary
upon changing the ion-mirror distance. Hence so-called vacuum forces,
due to the presence of the mirror, have been observed by measuring the
motional (or external) states of the ion. In the strictest sense the effects of
the mirror cannot be described by modified vacuum fields alone and the
ion’s own radiation reaction field must also be considered to be modified.
[1] M.A. Wilson et al., Phys. Rev. Lett. 91, 213602, (2003)
[2] J. Eschner et al., Nature 413, 495-498, (2001)