aktualisiertes pdf - DPG-Tagungen

odische imaginäre Potentiale können einfach für metastabile Atome realisiert
werden. Die ortsabhängige Absorption wird mit Hilfe einer stehenden
Lichtwelle realisiert, deren Frequenz auf einen angeregten Zustand
abgestimmt ist, der hauptsächlich in den Grundzustand zerfällt. Da nur
die metastabilen Atome nachgewiesen werden, entspricht die Absorption
eines Photons der Absorption (Vernichtung) eines metastabilen Atoms.
Wir werden im Detail den experimentellen Nachweis der vorhergesagten
Wellenpakete diskutieren. Mit Hilfe eines atom-interferometrischen
Aufbaus konnten wir sowohl den Absolutbetrag, als auch die räumliche
Phase des Wellenpakets vermessen. Die experimentellen Daten stimmen
sehr gut mit den theoretischen Vorhersagen[2] überein.
[1] D.O. Chudesnikov and V.P. Yakovlev, Laser Phys., 1, 110 (1991).
[2] M.A. Efremov et al., Laser Phys., 13, 995 (2003); JETP, 97, 522
(2003).
Q 25.3 Di 17:15 HS 218
Wellenpaketdynamik und Zahlenfaktorisierung — •Eric Lutz,
Holger Mack und Wolfgang P. Schleich — Universität Ulm, Abteilung
für Quantenphysik D-89069 Ulm
Die Zeitentwicklung eines Wellenpakets mit quadratischen Phasenfaktoren
zeigt quantenmechanische Wiederkehrphänomene, die als revivals
und fractional revivals bezeichnet werden. Wir zeigen wie diese fractional
revivals benutzt werden können um Zahlen zu faktorisieren und diskutieren
wie die einzelnen Faktoren aus der Messung der Autokorrelationsfunktion
gewonnen werden können.
Q 25.4 Di 17:30 HS 218
Coherent propagation of electron wavepackets in arrays of
coupled quantum dots — •Georgios Nikolopoulos 1,2 , David
Petrosyan 2 , and Peter Lambropoulos 2 — 1 Institut für Angewandte
Physik, Technische Universität Darmstadt, D-64289 Darmstadt
— 2 Institute of Electronic Structure and Laser, FORTH, P.O.Box 1527,
Heraklion, GR-71110 Crete
Quantum computing schemes where the qubits are represented by spinstates
of single electrons confined in individual quantum dots(QDs), are
of particular interest to current research, since they are considered to
be the most promising candidates for making large quantum computers.
Motivated by the necessity of understanding the dynamics of electron
wavepackets in the presence of disorder and dissipation and to investigate
the conditions under which coherent transport can be achieved,
we study the dynamics of few-electron transport in a linear array of
tunnel-coupled quantum dots. The electrons are considered initially well
localized at the ends of the chain and their spin-sates are well defined.
We find that this system exhibits a rich variety of coherent phenomena,
ranging from electron wavepacket propagation and interference to manyparticle
bonding and collision. Furthermore, we show that choosing the
couplings between adjacent QDs (optimal coupling) judiciously, one may
achieve non-dispersive propagation of the electron wavepacket. A possible
scenario capable of producing controllable mesoscopically separated
EPR correlated pairs of electrons is presented.
Q 25.5 Di 17:45 HS 218
Phase-Control of Collective Quantum Dynamics — •Jörg
Evers 1 , Mihai Macovei 1,2 , and Christoph H. Keitel 1 —
1 Theoretische Quantendynamik, Fakultät für Mathematik und Physik,
Universität Freiburg, Hermann-Herder-Str. 3, D-79104 Freiburg im
Breisgau — 2 Institute of Applied Physics, Academiei str. 5., MD-2028
Chisinau, Moldova
Ever since the classic work by Dicke [1], the concept of collectivity for
dipole-interacting atoms confined in a region of the order of a typical
optical wavelength has received considerable attention. However for possible
applications, convenient schemes are required to control the atoms.
In this talk, we present a control scheme based on the manipulation of
the relative phase between the driving laser fields [2] for a collection
of three-level atoms in V - or Λ- configuration [3]. For larger samples,
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the phase is shown to be a convenient parameter to rapidly populate or
depopulate completely a trapping state of the ensemble. Increasing the
number of atoms leads to a more rapid transfer of the atoms into the
trapping states or vice versa. As applications, we discuss fluorescence
and absorption properties of the atoms and a possible setup for a fast
optical switching device controlled by the relative phase.
[1] R. H. Dicke, Phys. Rev. 93, 99 (1954).
[2] M. A. G. Martinez et al., Phys. Rev. A. 55, 4483 (1997), E. Paspalakis
and P. L. Knight, Phys. Rev. Lett. 81, 293 (1998).
[3] M. Macovei, J. Evers and C. H. Keitel, Phys. Rev. Lett. 91, 233601
(2003).
Q 25.6 Di 18:00 HS 218
Exact decoherence to pointer states in free open quantum systems
is generic — •J. Eisert — Institut für Physik, Universität
Potsdam, Am Neuen Palais 10, D-14469 Potsdam
In this talk it is shown that exact decoherence to minimal uncertainty
Gaussian pointer states is generic for free quantum particles coupled to
a heat bath. More specifically, the paper is concerned with damped free
particles linearly coupled to a heat bath at arbitrary temperature, with
arbitrary coupling strength and spectral densities covering the ohmic,
subohmic, and supraohmic regime. Then it is true that there exists a time
tc such that for times t > tc the state can always be exactly represented as
a mixture (convex combination) of particular minimal uncertainty Gaussian
states, regardless of the initial state. This exact ‘localisation’ is hence
not only a feature of the high temperature and weak damping limit, but
rather a generic property of damped free particles.
Q 25.7 Di 18:15 HS 218
Measurement-based approach to quantum arrival times —
•Dirk Seidel and Gerhard C. Hegerfeldt — Tammannstrasse 1,
37077 Göttingen, Germany
For a quantum-mechanically spread-out particle we investigate a method
for determining its arrival time at a specific location. The procedure is
based on the emission of the first photon from a two-level system moving
into a laser-illuminated region. The resulting temporal distribution
is explicitly calculated for the one-dimensional case and compared with
axiomatically proposed expressions. As main results we show that (a) by
means of a deconvolution one obtains the well known quantum mechanical
probability flux of the particle [1] (b) by normalizing the corresponding
temporal operator function the axiomatic arrival-time distribution
of Kijowski is recovered [2] (c) a limiting case yields Allcock’s complex
potential model.
[1] J.A. Damborenea, I.L. Egusquiza, G.C. Hegerfeldt, J.G. Muga, Phys.
Rev. A 66, 052104 (2002)
[2] G.C. Hegerfeldt, D. Seidel, J.G. Muga, Phys. Rev. A 68, 022111 (2003)
Q 25.8 Di 18:30 HS 218
Analysis of a minimally invasive detector model — •Jens Timo
Neumann und Gerhard C. Hegerfeldt — Inst. f. Theor. Physik,
Univ. Göttingen, Tammanstr. 1, 37077 Göttingen
Recently, models (J.J. Halliwell, Progr.Theor.Phys. 102 No. 4
(1999), 707-717; L.S. Schulman, talk at 8 th Workshop on Time in Quantum
Mechanics, Teneriffe 2003) for minimally invasive particle detectors
have been proposed, similar to a cloud chamber where a charged particle
causes macroscopic changes in the environment without itself being
disturbed strongly. In the model, the detector (not the particle!) couples
to a large environment only when the wave function of the particle
overlaps with the detector. We investigate to what extent the model is
truly minimally invasive and show that it has a close relation to quantum
optics, with similar limitations as in the detection through fluorescence
by means of a laser. Possible optimization schemes are discussed.