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Reminder</title></head><body>
<div>This week's MIT QIP seminar will take place on Monday, November
1st at 16:00 in 4-237, and features:</div>
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<div align="center"><font size="+2"><b>How to Build a Quantum Computer
Out of Spin Chains</b></font></div>
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<div align="center"><font size="+1"><i>by</i> Andrew Landahl (<i>MIT
Media Lab</i>)</font></div>
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<div align="center"><u>ABSTRACT</u></div>
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<blockquote>Quantum circuits are built out of quantum wires and
quantum gates. For applications in which quantum bits are spins
packed at high density, like the hard drive of a quantum computer, it
is worthwhile to examine how well spin-spin interactions can implement
these wires and gates directly, without the need for external
dynamical control. In this talk I present spin networks of
Heisenberg and XY interactions that act as perfect quantum
wires---quantum states transfer across them with unit fidelity.
I show that perfect communication length scales logarithmically when
all bonds have the same strength, and how to engineer bond strengths
so that arbitrary length perfect quantum communication is possible.
I conclude by showing how to extend perfect quantum wires to perfect
quantum gates using some well-known ideas proven by Feynman in the
late 1980s.</blockquote>
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<div>Next Monday: Karol Zyczkowski (Visiting Scientist, Perimeter
Inst.) will be speaking "On the duality between quantum states
and quantum maps".</div>
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