April 2009 - ITP-quantumseminare

Research day next week
by Roger Colbeck 24 Jul '09

24 Jul '09

Hi all, (Beatrix, please advertise the second talk on the screens) There will be two talks next week. The first is in IFW D42 at 5pm by Joe Renes. I don't have a title yet. The second talk will be by Nilanjana Datta at 11am on Thursday in HIT K52 (abstract attached). See you there! Roger

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[QI] Seminar
by Dejan D. Dukaric 12 May '09

12 May '09

Dear All, Next weeks research day on Wednesday! will be at the Computer Science Building. Speaker: Bhavana Kanukurthi (Boston University) Title: "Key Agreement from Close Secrets over Unsecured Channels" Time: 5 pm Place: IFW E44 Abstract: Can you communicate securely with no public key infrastructure, strong secrets, and computational hardness assumptions? We consider information-theoretic key agreement between two parties sharing somewhat different versions of a secret w that has relatively little entropy. This setting arises, for example, when a trusted server stores the biometric of a user, and the user subsequently uses his fresh biometric reading to authenticate himself to the server. Such key agreement, also known as information reconciliation and privacy amplification over unsecured channels, was shown to be theoretically feasible by Renner and Wolf (Eurocrypt 2004), although no protocol that runs in polynomial time was described. We propose a protocol that is not only polynomial-time, but actually practical, requiring only a few seconds on consumer-grade computers. Our protocol can be seen as an interactive version of robust fuzzy extractors (Dodis et al., Crypto 2006). While robust fuzzy extractors, due to their noninteractive nature, require w to have entropy at least half its length, we have no such constraint. In fact, unlike in prior solutions, in our solution the entropy loss is essentially unrelated to the length or the entropy of w, and depends only on the security parameter. The paper appears in Eurocrypt 2009 and is available at http://eprint.iacr.org/2008/494. This is joint work with Leonid Reyzin. Cheers, Dejan

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Talk next week
by Stefan Wolf 29 Apr '09

29 Apr '09

Hi all, We will have a visitor next week, Bhavana Kanukurthi, a collaborator of Leonid Reyzin from Boston University. Bhavana will give a talk on Wednesday, May 6, at 5 pm in IFW E44. You are all very welcome to attend! Stefan __________________________________________________________________________ Title: Key Agreement from Close Secrets over Unsecured Channels Speaker: Bhavana Kanukurthi Affiliation: Boston University Can you communicate securely with no public key infrastructure, strong secrets, and computational hardness assumptions? We consider information-theoretic key agreement between two parties sharing somewhat different versions of a secret w that has relatively little entropy. This setting arises, for example, when a trusted server stores the biometric of a user, and the user subsequently uses his fresh biometric reading to authenticate himself to the server. Such key agreement, also known as information reconciliation and privacy amplification over unsecured channels, was shown to be theoretically feasible by Renner and Wolf (Eurocrypt 2004), although no protocol that runs in polynomial time was described. We propose a protocol that is not only polynomial-time, but actually practical, requiring only a few seconds on consumer-grade computers. Our protocol can be seen as an interactive version of robust fuzzy extractors (Dodis et al., Crypto 2006). While robust fuzzy extractors, due to their noninteractive nature, require w to have entropy at least half its length, we have no such constraint. In fact, unlike in prior solutions, in our solution the entropy loss is essentially unrelated to the length or the entropy of w, and depends only on the security parameter. The paper appears in Eurocrypt 2009 and is available at http://eprint.iacr.org/2008/494. This is joint work with Leonid Reyzin. -------------------------------------------------------------------------------

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[QI] QI Seminar
by Dejan D. Dukaric 22 Apr '09

22 Apr '09

Dear All, Next weeks research day on Tuesday will be at Hoenggerberg. Speaker: Joonwoo Bae Title: "Structural physical approximations to positive maps and entanglement breaking channels" Time: 28.4.09 at 5 pm Place: HIT K 51 Abstract: Structural approximations to positive, but not completely positive maps are approximate physical realizations of these nonphysical maps. They find applications in the design of direct entanglement detection methods. We show that many of these approximations, in the relevant case of optimal positive maps, define an entanglement breaking channel and, consequently, can be implemented via a measurement and state preparation protocol. We also show how our findings can be useful for the design of better and simpler entanglement detection methods. Cheers, Dejan

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[QI] QI Seminar
by Dejan D. Dukaric 20 Apr '09

20 Apr '09

Dear All, Here is the title and abstract of tomorrows talk: Speaker: Johan Aaberg Title: "Depletion forces" Time: 5 pm Place: IFW D42 Abstract: In lack of anything more exciting to say I will talk about depletion forces. I am not going to spoil the story by telling in advance what it is about, but I will keep the talk short, light, and purely classical. Cheers, Dejan

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[QI] QI Seminar
by Dejan D. Dukaric 20 Apr '09

20 Apr '09

Dear All, This weeks research day on Tuesday will be at the Computer Science Building. Speaker: Johan Aaberg Title: TBA Time: 5 pm Place: IFW D42 Abstract: TBA Cheers, Dejan

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talk tomorrow
by Roger Colbeck 06 Apr '09

06 Apr '09

Hi all, Tomorrow we have an external visitor, Stefano Chesi from Basel who will give a talk at 5pm in HIT K51 on "Quantum Hall ferromagnetic states and spin-orbit interactions in the fractional regime". Abstract: The competition between the Zeeman energy and the Rashba and Dresselhaus spin-orbit couplings is studied for fractional quantum Hall states including correlation effects. A transition of the direction of the spin-polarization is predicted at specific values of the Zeeman energy. We show that these values can be expressed in terms of the pair-correlation function, which thus provides a way to obtain experimental access to the corresponding ground state. As specific examples, we consider the Laughlin wavefunctions and the 5/2-Pfaffian state and find indications of non-analytic features around the fractional states. We also include effects of the nuclear bath, becoming relevant in the mK-regime. Roger

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[QI] QI Seminar
by Dejan D. Dukaric 03 Apr '09

03 Apr '09

Dear All, There wont be a seminar talk the next two times due to the Easter break. The seminar will start again on 21.4. with a talk given by Johan. Cheers, Dejan

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