June 2014 - ITP-quantumseminare - lists.phys.ethz.ch

today's group meeting E41.1 @ 4pm
by Joe Renes 10 Jun '14

10 Jun '14

Hi all, today we'll meet at 4pm in E41.1 to hear from Cyril Stark, back to visit from MIT. Here is a preview of his talk: Title: "About the role of compression in quantum tomography" Abstract: Assume we are considering an experiment which allows us to prepare unknown states and to perform unknown measurements. An effective model for this experiment is both a description of each state in terms of a density matrix and a description of each measurement in terms of a POVM. Different models can be assigned to the same measurement data. To pick a specific model from the set of candidate models, we try to find a model which is compatible with the measured data, i.e., the measured frequencies for different measurement outcomes are well approximated by the probabilities predicted by Born's rule. In this talk I will discuss robustness of the Hilbert space dimension of quantum models. More precisely, by the definition of an explicit compression scheme, I will show that quantum models can be compressed into lower-dimensional quantum models if the measured data is noisy (e.g., due to finite-size effects). Of course, the compressed model fits the measured data not as well as the original model. When we compress into a model whose dimension is only poly-logarithmic in the dimension of the original model, then the error grows linearly in the trace norm of the POVM elements of the original model. Here, the error is quantified in terms of the max norm distance between measured frequencies and predictions in terms of Born's rule. It follows, for example, that d-dimensional models involving only projective and non-degenerate measurements admit compression into models of dimension O(poly(log(d))). This is joint work with Aram Harrow. Best, -joe

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today's meeting postponed / replaced with soccer (go team!)
by Joe Renes 02 Jun '14

02 Jun '14

Hi all, in view of the fact that many group members are away or participating in the Boltzmann cup, today's meeting is postponed till next week. Cyril Stark will be visiting and will tell us about his latest research. Best, -joe

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Reminder: QSIT Lunch Seminar - Lea Kraemer and Benedikt Herzog - Thursday June 5, 2014
by QSIT Seminar 02 Jun '14

02 Jun '14

Dear QSIT members The next QSIT Lunch Seminar will take place on Thursday June 5, 2014 at 12:00 noon in the room HPF G 6, ETH Zurich, Hönggerberg. There will be two talks of 30 minutes duration jointly presented by two collaborators from different research groups. At 13:00 pm free lasagna is offered to the participants. Boundary between the Thermal and Statistical Polarization Regimes in a Nanometer-scale Spin Ensemble Benedikt Herzog Spin, Quantum Electronics, Nanomechanics - Poggio Lab, University of Basel and Entropies in thermodynamics and information theory: a new approach Lea Krämer Quantum Information Theory, ITP, ETH Zurich Abstracts at: http://www.nccr-qsit.ethz.ch/news/lunchseminar/june2014 Please register for your free Lasagna at the following link by Tuesday June 3, 12:00 noon https://ethz.doodle.com/vs4bzagcawawud48 If you have suggestions on topics or speakers, or would like to present recent results of your research, please send your information to Andreas Wallraff or Ilona Blatter. With best regards, Andreas Wallraff, Professor for Solid State Physics Ilona Blatter QSIT Office ------------------------------------------------------------------------------------------------------ ETH Zurich Dr. Ilona Blatter NCCR QSIT Coordinator Laboratory for Solid State Physics HPF E 17 Otto-Stern-Weg 1 8093 Zurich ilona.blatter(a)phys.ethz.ch www.nccr-qsit.ethz.ch Phone: +41 44 633 36 06

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