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<div>This week's MIT QIP seminar will take place on Monday, October 27
at 16:00 hours in room 4-270, and features:</div>
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<div align="center"><font size="+2"><b>Wehrl Entropy, the Lieb
Conjecture and Entanglement Monotones</b></font></div>
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<div align="center"><font size="+1">by Prof. Karol
Zyczkowski</font></div>
<div align="center"><font size="+1"><i>Smoluchowski Institute of
Physics, Jagiellonian University, Cracow</i></font></div>
<div align="center"><font size="+1">and<i> Center for Theoretical
Physics, Warsaw, Poland</i></font></div>
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<div align="center"><u>ABSTRACT</u></div>
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<blockquote>Wehrl entropy, defined as the average entropy of the
Husimi function, may be used to quantify the localization of any
quantum state in the phase space. The coherent states are as much
localized in phase space as possible. In a finite-dimensional Hilbert
space one defines the SU(2) spin-coherent states, and according to the
Lieb conjecture their Wehrl entropy of is minimal in the set of all
(mixed) states. The same conjecture may be formulated for higher,
SU(N) coherent states.</blockquote>
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<blockquote>We define the Wehrl entropy for the states of a quantum N
x N composite system computed with respect to SU(N) coherent states. A
pure state of the composite system displays the minimal Wehrl entropy
if and only if it is a product state. Hence the entropy excess (the
difference with respect to the minimal entropy) may thus characterize
quantitatively the entanglement of the state. We prove that this
quantity is indeed an entanglement monotone and show a link with the
quantum subentropy defined by Jozsa, Robb and Wootters. The Wehrl
entropy excess can be generalized for the multipartite
systems.</blockquote>
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