[QIP-Sem] MIT QIP Seminar Announcement

[QIP-Sem Mailing List]

Next week's MIT QIP seminar will take place on Monday, October 27 at 
16:00 hours in room 4-270, and features:


Wehrl Entropy, the Lieb Conjecture and Entanglement Monotones

by Prof. Karol Zyczkowski
Smoluchowski Institute of Physics, Jagiellonian University, Cracow
and Center for Theoretical Physics, Warsaw, Poland

ABSTRACT

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.

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.

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