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     COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
   AND THE SCHOOL OF PHYSICS, ASTRONOMY AND COMPUTATIONAL SCIENCES
                       (CSI 898-Sec 001)
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       Quantum Computing Based on Josephson-Junction SQUID Phase 
          Qubits Qubits Representations and Coherence Time
 
                     J. Robert Anderson 
Department of Physics, University of Maryland, College Park, MD

Quantum computing based on many different types of qubits has developed into
an important field of research. A quantum computer with its entangled qubits
should provide a much more efficient technique for specific tasks such as
finding prime factors of large numbers, searching a non-structured data base,
and finding the solution of a very large number of linear equations. Our
financial security depends on our inability to find  the factors of large
integers, which are used for encryption. We are investigating the use of
Josephson junctions in a superconducting quantum interference device (SQUID)
configuration for these qubits. For success, the time for logic gate
operations must be shorter than the coherence times of entangled qubits. In
this talk the basic physics of Josephson junction qubits will be described and
a review of our experiments to make better junctions and to study and
eliminate the sources of decoherence will be presented. Investigations of
coherence times via Rabi oscillations and the Ramsey effect will be shown and
the reasons for using a SQUID phase qubit will be discussed. In addition, the
combination of trapped atoms and Josephson junctions, a possible improvement
over the use of these techniques separately, will be described. We have
obtained a significant improvement in coherence times during the last few
months and these recent results will be presented.

                      Monday, April 18, 2011
                               4:30 pm
                    Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at http://cmasc.gmu.edu/seminar/schedule.html