May 2009 - ITP-quantumseminare - lists.phys.ethz.ch

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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Next week
by Roger Colbeck 22 May '09

22 May '09

Hi all, Next week Scott Aaronson is visiting from MIT (the ETH of North America). He will give a talk on Tuesday at 5pm in HIT K51 (probably on quantum copy-protection and quantum money). Then on Wednesday he will give the Physics Colloquium (see http://www.colloquium.phys.ethz.ch/ for details). Hope you can make it. Roger

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[QI] Seminar
by Dejan D. Dukaric 19 May '09

19 May '09

Dear all, We have changed the room, it's now in IFW D 42 (still starting at 4 pm). Cheers, Dejan

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today's talk postponed until tomorrow
by Roger Colbeck 13 May '09

13 May '09

Hi all, This afternoon's talk has been postponed to tomorrow morning at 10:30 in HIT K52. David Gross will speak on "The failure of highly entangled states to be useful for measurement-based quantum computation and the failure of infinite-dimensional models to respect Lieb-Robinson bounds." Abstract: I will give a black board talk on two totally unrelated results, emphasizing (or dropping) the one or the other based on the audience's demands. In the first part, I show that measurement-based computation on quantum states with a high value of the geometric measure of entanglement can be classically efficiently simulated. It is further shown that generic states are subject to this effect. A slightly over-simplified summary reads "Most quantum states are too entangled to be useful". The argument is mostly elementary and can be completely proved in a black board session without putting too much strain on the audience's attention. The second topic concerns information propagation in many-body systems. In finite-dimensional spin chains, localized perturbations propagate no faster than a given "speed of sound" characteristic of the system's Hamiltonian. This fact, known by the name of Lieb-Robinson bound, plays a surprisingly fundamental role in many rigorous arguments ascertain classical simulatability of some many-body systems. One could expect similar results to hold even for infinite-dimensional systems in the presence of energy constraints. However, we construct a drastic counter-example to any such conjecture. References: arXiv:0810.4331, arXiv:0808.3581. Cheers, 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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change of talk time
by Roger Colbeck 12 May '09

12 May '09

Hi all, This Thursday's talk by Barbara Kraus has been moved to 4pm due to a clash. Both talks this week are in HIT K51 (which I forgot to mention in the last mail). Cheers, Roger

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This week
by Roger Colbeck 11 May '09

11 May '09

Hi all, This week the research day will be on Wednesday with a talk by David Gross at 3pm, title to be decided. There will be an additional talk by Barbara Kraus at 3pm on Thursday: Quantum State Preparation using dissipation We investigate the possibility of using a dissipative process to prepare a quantum system in a desired state. We derive for any multipartite pure state a dissipative process for which this state is the unique stationary state and solve the corresponding master equation analytically. For certain states, like the Cluster states, we use this process to show that the jump operators can be chosen quasi--locally, i.e. they act non--trivially only on a few, neighboring qubits. We demonstrate the general formalism by considering MPS--PEPS states. In particular, we show that the ground state of the AKLT-model can be prepared employing a quasi-local dissipative process. Furthermore, we discuss a dissipatively driven Bose-Einstein Condensate, where for non-interacting atoms a pure state exhibiting long range order is generated as the steady state by quasi-local coupling to an environment with finite correlation length. Applying standard linearization schemes in the weakly interacting situations, allows us to determine the solution of the master equation, revealing a steady state with properties similar to bosons in thermal contact to a heat bath. Furthermore, we consider a special class of states, called locally maximally entangleable states and discuss their applications for quantum information tasks. The generation of those states using either dissipative processes, or unitary evolutions is presented. Cheers, Roger

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dinner tonight
by Stefan Wolf 07 May '09

07 May '09

good morning, we are going for dinner with bhavana tonight, say at 7pm. you are very welcome to join! please let me know whether you would like to come, so we can decide what is a good place to go and make a reservation. thank you. stefan

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