aktualisiertes pdf - DPG-Tagungen

Q 22.15 Di 14:00 Schellingstr. 3
Simulation of Quantum Computations by using Maple —
•Thomas Radtke and Stephan Fritzsche — Universität Kassel,
34281 Kassel, Germany
During the last years, the topics of quantum information and computation
have attracted a lot of interest. However, apart from the great
potential of their applications, they gave rise to a large number of theoretical
and experimental questions which still need to be resolved. Popular
examples of quantum algorithms like the well-known factorization algorithm
for prime numbers by Peter Shor may give a first impression of
what quantum computation might be able to do in the future [1].
But for the further analysis of algorithm capabilities and their efficiency,
new tools are needed. That is why several simulators for quantum
computations have been developed in the past. In order to improve the
flexibility of user interaction, we recently started to develop our Feynman
program within the framework of Maple. At present, it consists
of a set of procedures which offer symbolic and numeric evaluation and
manipulation of quantum bits, quantum registers and matrix operators.
For the future we plan to extend the program to simulate also quantum
algorithms for different physical realizations of quantum computers. We
hope that this will enable us to investigate problems that are connected
Q 23 Quanteninformation II
to decoherence and robustness in multi-qubit systems [2].
[1] M. A. Nielsen, I. L. Chuang, Quantum Computation and Quantum
Information (Cambridge University Press, Cambridge, 2000).
[2] A. W. Harrow, M. A. Nielsen, Phys. Rev. A 68, 012308 (2003).
Q 22.16 Di 14:00 Schellingstr. 3
Quantum Error Correction with Multiple-Error Correcting
Quantum Code s — •Gernot Alber and Jörg Wassenberg —
Institut für Angewandte Physik, Technische Universität Darmstadt,
Hochschulstraße 4a, D-64289 Darmstadt
In order to perform computations with a quantum computer it is necessary
to stabilize the computer’s memory against decoherence over a
sufficiently large time scale. If the qubits are represented by electronic
levels of atoms or ions an important error source is spontaneous emission.
Encoding the information in a detected-jump correcting quantum code, errors
can be corrected by application of suitable recovery operations upon
detection of spontaneous emission events.
We study the stabilizati on of quantum algorithms against spontaneous
emission by jump codes being capable of correcting two or more successive
errors, and compare with exist ing results using one-error correcting
codes.
Zeit: Dienstag 16:30–18:30 Raum: HS 101
Q 23.1 Di 16:30 HS 101
Quasi decoherence-free subspaces in collective quantum memories
— •C. Mewes, R.G. Unanyan, and M Fleischhauer — Fachbereich
Physik, Universität Kaiserslautern, 67653, Kaiserslautern, Germany
One of the most important practical challenges of quantum information
processing is the protection of quantum information against decoherence.
For photonic qubits stored in collective atomic superpositions
[1] it can be shown that the quantum information can be protected from
individual particle decoherence by combining dynamical decoupling well
known in NMR systems, e.g.[2], with the concept of quasi-decoherence
free subspaces. For the storage of qubits a pair of special collective states
is used in which the qubit is stored in two different magnetic sublevels.
Individual collisional interactions between the storage atoms itself and
foreign buffer gas perturbers lead to decoherence due to spin flips and
dephasing processes. By applying a fast periodic interaction it is possible
to supress the dephasing mechanism. To protect the system also against
spin flips an additional and sufficiently large energy gap between the two
storage states and all other states has to be introdu! ced. In this way the
stored qubit can be protected against decoherence from both spin flips
and dephasing [3].
[1] M. Fleischhauer and M. Lukin, PRL 84 (2000) 5904
[2] U. Haeberlen and J.S. Waugh, Phys. Rev. 175 (1968) 453
[3] C. Mewes, R. Unanyan and M. Fleischhauer. To be published
Q 23.2 Di 16:45 HS 101
Quantum phase gate using slow polaritons in optical lattices —
•Marius Masalas 1,2 and Michael Fleischhauer 1 — 1 Technische
Universität Kaiserslautern, Germany — 2 Institute of Theoretical Physics
and Astronomy, Vilnius University, Lithuania
The quantum state of light propagating in a medium with electromagnetically
induced transparency can be mapped onto a matter wave. Using
elastic collisions between atoms and slow light techniques one can produce
a large and controllable nonlinearity enhanced by an optical lattice.
This nonlinearity may be used for a quantum phase gate. The collision
problem of two polariton pulses, each containing a single excitation is
solved analitically and it is shown that it is possible to achieve phase
shift of order of π. The influence of degrading processes such as losses is
also discussed.
103
Q 23.3 Di 17:00 HS 101
Licht-Materie Schnittstelle für kontinuierliche Variable —
•Klemens Hammerer 1 , Klaus Mölmer 2 , Eugene Polzik 3
und Ignacio Cirac 1 — 1 Max-Planck-Institut für Quantenoptik,
Hans-Kopfermannstrasse 1, D-85748 Garching — 2 QUANTOP, Danish
Research Foundation Center for Quantum Optics 3 Department of
Physics and Astronomy, University of Aarhus, DK 8000 Aarhus C,
Denmark — 3 Niels Bohr Institute, DK 2100 Copenhagen, Denmark
Wie bereits experimentell bestätigt, kann eine Kerr Wechselwirkung
zwischen einem Spin-polarisierten Ensemble von Zwei-Niveau-Atomen
und einem polarisierten Laserpuls dazu eingesetzt werden, verschränkte
Zustände zwischen diesen Systemen zu erzeugen. Wir zeigen hier, wie der
Effekt dieser Wechselwirkung um ein Vielfaches gesteigert werden kann.
Die Methode, die hier vorgestellt werden soll, erlaubt es, gezielt maximal
verschränkte EPR Zustände oder Quadratur- und Spin-gequetschte
Zustände herzustellen.
Diese Zustände stellen eine wertvolle Resource dar für Zwecke der
Quanteninformation. Insbesondere kann ein EPR-Zustand dazu verwendet
werden, einen unbekannten Polarisationszustand eines Lichtpulses
auf den Zustand des kollektiven Spins der Atome zu teleportieren. Weil
Licht einen idealen Träger zum Verteilen von Quantenzuständen bildet,
zum Speichern dieser Zustände aber Atome besser geeignet sind, ist eine
solche Schnittstelle zwischen Licht und Materie ein wichtiger Baustein
für ein Quantennetzwerk.
Q 23.4 Di 17:15 HS 101
Multiparticle entanglement generation using ground states
coherences — •Pavel Lougovski 1 , Girish. S. Agarwal 2 , and
Herbert Walther 1 — 1 Max-Planck-Institut für Quantenoptik,
Hans-Kopfermann-Str. 1, D-85748, Garching, Germany — 2 Physical
Reaserch Laboratory, Navrangpura, Ahmedabad, India
We propose a method for the generation of multiparticle ground state
entanglement utilizing j=+1/2 to -1/2 atomic transitions and their interaction
with far detuned elliptically polarized quantum field. We discuss
how this method could be used for storing and retrieving of quantum
states of the radiation field.
Q 23.5 Di 17:30 HS 101
Entanglement of formation versus negative domains of Wigner
functions. — •Alexander Wolf 1 , Jens Peder Dahl 2 , and Wolfgang
Peter Schleich 1 — 1 Abteilung für Quantenphysik, Universität
Ulm, D-89069 Ulm, Germany — 2 Chemical Physics, Department
of Chemistry,Technical University of Denmark, DTU 207, DK-2800 Kgs.
Lyngby, Denmark
We analyze entanglement of formation and negative domains of Wigner
functions in their dependence on the number of dimensions. Here, we focus
on s-waves, that is, wave functions that only depend on a hyperradius.