July 2010 - ITP-quantumseminare - lists.phys.ethz.ch

quantum information theory talk
by Matthias Christandl 27 Jul '10

27 Jul '10

Dear all, next week, Stefan Bäuml, who has just finished his diploma at LMU in Munich will be giving the following talk: Tuesday, 3rd August, 11am, HIT K 51 Speaker: Stefan Bäuml Title: On bound key and the use of bound entanglement Abstract: While bound entanglement turned out to be potentially useful for some practical tasks such as quantum key distribution, it is not known whether entanglement swapping using bound entangled states can result in a state that is still entangled. In this talk, the question will be addressed for several examples. In addition to that, a lower bound on the dimension of bound entangled states approximating private states will be presented. This talk will also contain some thoughts on the so far unanswered question whether, analogously to bound entanglement, there exists bound key. A possible definition of key cost will be introduced and its implications discussed. Best wishes, Matthias. Matthias Christandl Institute for Theoretical Physics ETH Zurich

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dinner
by Matthias Christandl 15 Jul '10

15 Jul '10

Dear all, we will go for dinner with our guests Graeme and Alonso tonight at 8pm to Maison Blunt which lies at Gasometerstrasse 5, 8005 Zürich. http://maps.google.ch/maps?hl=de&client=safari&ie=UTF8&q=maison+blunt&fb=1&… The following people have signed up so far: Miriam Oscar? Fred Alonso Graeme Johan Matthias Renato? I have reserved a table for eight. You are still most welcome to join, just send me an email and I will get a bigger table. All the best, Matthias. Matthias Christandl Institute for Theoretical Physics ETH Zurich

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quantum information theory talks
by Matthias Christandl 09 Jul '10

09 Jul '10

Dear all, all of next week we have two visitors who study entanglement with methods from representation theory. They will each give a talk, which I herewith announce. Tuesday, 13th July, 11am, HIT K 51 Speaker: Graeme Mitchison Title: The structure of local unitary invariants for qubit states. Abstract: Local unitary invariants, i.e. real-valued functions of states that are invariant under local unitary action, can be regarded as entanglement measures. They have a rich structure, even for pure n-qubit states. I show that there is a fundamental family of invariants based on polynomials called cumulants. They have nice properties and account for about half of the total number for a complete set of invariants. They also have a hierarchical structure related to tracing out subsystems. I argue that this helps us understand the whole set of invariants and casts light on entanglement. Wednesday, 14th July, 11am, HIT K 51 Speaker: Alonso Botero Title: Weyl-Schur duality and asymptotic multipartite entanglement Abstract: Through the so-called Weyl-Schur decomposition of n-fold tensor product Hilbert spaces, it is possible to connect various asymptotic rates of significance in Quantum Information Theory with the dimensions of certain "typical" invariant subspaces carrying irreducible representations of the permutation group. In this talk, I suggest a framework for the analysis of multipartite entanglement based on a similar application of the Weyl-Schur decomposition to the n-fold product of a multipartite state. Within this framework, it is possible to connect LU and SLOCC invariants to asymptotic rates and other quantities having a clear operational significance in terms of the resulting "typical" entanglement structures. These structures also suggest interesting connections between multipartite entanglement concentration, certain structures in algebraic combinatorics (Kronecker coefficients, Planar Transport problems, Association Schemes, etc.), and the theory of discrete orthogonal polynomials. I will try to give a brief overview of these connections and some partial results we have obtained in the three-qubit case. Best wishes, Matthias. Matthias Christandl Institute for Theoretical Physics ETH Zurich

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