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--></style><title>MIT Quantum Information Processing Seminar
Announcement</title></head><body>
<div>This week's MIT QIP seminar will take place on Monday, Nov.<b>
29</b> at 16:00 in 4-237, and features:</div>
<div><br></div>
<hr>
<div align="center"><font size="+2"><b>Quantum Information Processing
with Trapped Ca+ Ions</b></font></div>
<div align="center"><br></div>
<div align="center"><font size="+1">by Prof. Rainer Blatt
<</font>Rainer.Blatt@uibk.ac.at<font size="+1">></font></div>
<div align="center"><br></div>
<div align="center"><i>Institut für Experimentalphysik,
Universität Innsbruck, Technikerstraße 25, A-6020 Innsbruck,
Austria,</i></div>
<div align="center">and</div>
<div align="center"><i>Institut für Quantenoptik und
Quanteninformation, Österreichische Akademie der Wissenschaften,
Technikerstraße 25, A-6020 Innsbruck, Austria.</i></div>
<div align="center"><br></div>
<div align="center"><u>ABSTRACT</u></div>
<div><br></div>
<blockquote>Trapped strings of cold ions provide an ideal system for
quantum information processing. The quantum information can be stored
in individual ions and these qubits can be individually prepared, the
corresponding quantum states can be manipulated and measured with
nearly 100% detection efficiency. With a small ion-trap quantum
computer based on two and three trapped Ca+ ions as qubits we have
generated in a pre-programmed way genuine quantum states. In
particular, entangled states of two particles, i.e. Bell states [1],
and of three particles, i.e. GHZ and W states [2], were generated
using an algorithmic procedure and their decoherence was investigated.
These states are of particular interest for the implementation of a
three-ion quantum register: we have demonstrated selective read-out of
single qubits (while protecting the other qubits) and manipulation of
single qubits of the register conditioned on the read-out results. The
generated states have been measured experimentally using a technique
known as state tomography allowing the population and phase of the
quantum system to be mapped. Moreover, quantum teleportation with
trapped ions was implemented [3] and can be used as resource for the
transfer of quantum information as well as for quantum information
processing.</blockquote>
<div><br></div>
<blockquote><font size="-1">[1] C. F. Roos, G. P.T. Lancaster, M.
Riebe, H. Häffner,W. Hänsel, S. Gulde, C. Becher, J. Eschner, F.
Schmidt-Kaler, and R. Blatt, Phys. Rev. Lett. 92, 220402
(2004).</font></blockquote>
<blockquote><font size="-1">[2] C. F. Roos, M. Riebe, H. Häffner, W.
Hänsel, J. Benhelm, G. P. T. Lancaster, C. Becher, F. Schmidt-Kaler,
and R. Blatt, Science 304, 1478 (2004).</font></blockquote>
<blockquote><font size="-1">[3] M. Riebe, H. Häffner, C. F. Roos, W.
Hänsel, J. Benhelm, G. P. T. Lancaster, T. W. Körber, C. Becher,
F. Schmidt-Kaler, D. F. V. James, R. Blatt, Nature 429, 734
(2004).</font></blockquote>
<div><font size="-1"><br></font></div>
<hr>
<div>Next week's feature: Robert Schoelkopf from Yale Univ. will speak
on "Circuit Quantum Electrodynamics: Doing Quantum Optics with
Superconductors".</div>
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