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Q 22 Poster Quanteninformation, -kommunikation und -computer
Zeit: Dienstag 14:00–16:00 Raum: Schellingstr. 3
Q 22.1 Di 14:00 Schellingstr. 3
Addressing of individual neutral atoms — •Igor Dotsenko, Dominik
Schrader, Yevhen Miroshnychenko, Mkrtych Khudaverdyan,
Stefan Kuhr, Wolfgang Alt, Arno Rauschenbeutel,
and Dieter Meschede — Institut für Angewandte Physik, Universität
Bonn, Wegelerstr. 8, 53113 Bonn
We have experimentally solved the problem of addressing individual
neutral atoms from a string of atoms stored in a standing wave
dipole trap. We apply a magnetic field gradient to produce a positiondependent
shift of the atomic hyperfine transitions. Using an intensified
CCD-camera we spatially resolve atoms and get information about their
positions [1]. The population of each atom is coherently transferred by
applying microwave radiation at the corresponding resonance frequency
of the atom [2].
By applying spectrally narrow pulses the population of a neighbouring
atom is not affected if the atomic separation is larger than ∼ 2µm.
The coherence properties of the atoms are characterized by observing
Rabi oscilations which show no contrast decay within measurement time
of 200 µs. Using spin-echo technique the decoherence time T2’ was determined
to be of the order of 500 µs. The presented results show the
realization of a ’quantum register’ built of single neutral atoms for storing
quantum information.
[1] Y. Miroshnychenko et al., Optics Express [in print] [2] D. Schrader
et al., in preparation
Q 22.2 Di 14:00 Schellingstr. 3
Finite size effects in entangled rings of qubits — •Tim Meyer,
Uffe V. Poulsen, Kai Eckert, Maciej Lewenstein, and Dagmar
Bruss — Universit”at Hannover
We study translationally invariant rings of qubits with a finite number
of sites N, and find the maximal nearest-neighbor entanglement for
a fixed z component of the total spin. For small numbers of sites our
results are analytical. The use of a linearized version of the concurrence
allows us to relate the maximal concurrence to the ground state energy
of an XXZ spin model, and to calculate it numerically for N¡25. We point
out some interesting finite-size effects. Finally, we generalize our results
beyond nearest neighbors.
Q 22.3 Di 14:00 Schellingstr. 3
Statistical mechanics of entanglement — •Jarek Korbicz, Florian
Hulpke, and Maciej Lewenstein — Institut für Theoretische
Physik, Universität Hannover, Appelstr. 2, 30167 Hannover, Germany
We apply the methods of statistical mechanics to the study of entanglement.
We consider the space of decompositions of a given density
matrix. In this space we introduce a polynomial cost-function, minimized
by decompositions composed entirely of projectors onto product vectors.
We next assume that the number of terms in each decomposition is large
and define an analog of a canonical partition function. We study it analytically
and numerically for a family of Werner states of two qubits.
Q 22.4 Di 14:00 Schellingstr. 3
Multi-party entanglement detection in spin chains with simple
measurements — •Geza Toth — Max Planck Institute for Quantum
Optics,Theoretical Division,Hans-Kopfermann-Strasse 1., Garching,
Germany D-85748
It is discussed what the minimum requirements are for entanglement
detection in a chain of spins, if the spins cannot be accessed individually.
The methods presented detect entangled states close to a cluster
state and a many-body singlet state, and might be viable for realization
in optical lattices of two-state bosonic atoms. The entanglement criteria
are based on entanglement witnesses, and also on the uncertainty of
collective observables.
Q 22.5 Di 14:00 Schellingstr. 3
Towards integrated micro-optics on atom chips — •Albrecht
Haase 1 , Thomas Fernholz 1 , Sönke Groth 1 , Christian Hock 1 ,
Peter Horak 2 , Bruce Klappauf 2 , Michael Schwarz 1 , Alexander
Stelzer 1 , Marco Wilzbach 1 , and Jörg Schmiedmayer 1
— 1 Physikalisches Institut, Universität Heidelberg, 69120 Heidelberg
— 2 Optoelectronics Research Centre, University of Southampton,
Southampton SO17 1BJ, UK
To develop the atom chip towards an universal tool for quantum information
processing, we explore the possibility of integrating micro-optical
components for the preparation, manipulation, and detection of atomic
qubit states. As a promising technique we investigate in detail the feasibility
of an on-chip optical fibre cavity. We describe fabrication, alignment,
and first experiments and give an outlook on further integration steps.
The experiment is funded by the Landesstiftung Baden-Württemberg
and the EU (ACQP collaboration).
Q 22.6 Di 14:00 Schellingstr. 3
Time-bin entangled single photons from a cavity-QED source
— •T. Wilk, T. Legero, M. Hennrich, A. Kuhn, and G. Rempe
— Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-
85748 Garching, Germany
Entangled photons are an indispensable ingredient of many quantum
information schemes. Most applications use polarisation entangled photons,
while others employ time-bin entanglement [1]: a single-photon
wave-packet is distributed over two distinct intervals which are separated
in time. In contrast to former experiments, where the time-bin entanglement
is realised by sending a single photon through a Mach-Zehnder
interferometer with unbalanced arms, we here present a single-photon
generation scheme that directly delivers such photons.
The photons emerge from a cavity-QED source, where a single atom
undergoes an adiabatic passage, driven by the ambient cavity and pumping
laser pulses [2]. Any variation of the amplitude of the laser pulses
affects the emission probability and has a direct impact on the shape
of the single-photon wave-packets. Therefore arbitrary shaping of timebin
entangled photons seems possible. We investigate whether the relative
phase between the two time bins can be controlled by appropriately
changing the phase of the driving laser. The degree and lifetime of a
possible entanglement, can be determined by time-resolved two-photon
interference [3].
[1] Brendel et al. Phys. Rev. Lett. 82, 2594 (1999)
[2] Kuhn et al. Phys. Rev. Lett. 89, 67901 (2002)
[3] Legero et al. Appl. Phys. B77, 797 (2003)
Q 22.7 Di 14:00 Schellingstr. 3
Creating and Measuring a coherent superposition in metastable
Neon — •Ulrich Schneider, Frank Vewinger, Manfred
Heinz, Ruth Garcia Fernandez, and Klaas Bergmann — Fachbereich
Physik TU Kaiserslautern
We demonstrate a technique, suitable for neutral atoms in an atomic
beam, that allows the preparation of a superposition state in an efficient
and robust way with a predetermined relative phase. For the preparation
we use the tripod-STIRAP scheme [1] applied to the creation of a coherent
superposition of two mj-states of the metastable state 3 P2 of Neon
atoms [2]. We also measure the relative phase of the two mj-components
of the superposition state about 16mm downstream of the preparation
region. The measurement is based on the mapping of the relative phase
into the population of the excited state as a function of the polarization
angle of a probe laser. We report data concerning the superposition of
the pairs of levels mj = +1 and mj = −1 as well as mj = −2 and mj = 0.
[1]:R.Unanyan et.al. Opt.Comm. 155, 144-154
[2]:F.Vewinger et al, PRL 91, 213001
Q 22.8 Di 14:00 Schellingstr. 3
Decoherence suppression in collective quantum memories —
•C. Mewes, R.G. Unanyan, and M Fleischhauer — Fachbereich
Physik, Universität Kaiserslautern, 67653, Kaiserslautern, Germany
An important question when discussing the application of many-atom
systems to quantum memory is sensitivity to errors and the question how
to suppress decoherence mechanisms. It is shown that photonic qubits
stored in collective atomic excitations can be protected from decoherence
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