Theory Seminar

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About the Theory Seminar

New Rules (since May 2012), Old rules

Contact: johannes.kofler@mpq.mpg.de


Date Seminars 2015   (Go to Seminars 2014, Seminars 2013, Seminars 2012, and earlier therein)


14.01.2015 Macrorealism

Lucas Clemente

Macrorealism — the world view that physical properties of macroscopic objects exist independent of measurements and are not influenced by them — has recently been a focus of both theoretical and experimental work in quantum physics. As experiments get closer to showing quantum superpositions of macroscopically distinct states, it becomes interesting to look at conditions for macrorealism beyond the well-known Leggett-Garg inequalitites. In this talk I will discuss a condition called no-signaling in time, that, in the right combination, can serve not only as a necessary, but also as a sufficient condition. We will show how to apply these conditions to physical experiments, and construct a definition for the classicality of quantum measurements and Hamiltonians. The talk's slides can be found at https://clemente.io/macrorealism.


21.01.2015 Area laws and efficient descriptions of quantum many-body states

Yimin Ge

It is commonly believed that area laws for entanglement entropies imply that a quantum many-body state can be faithfully represented by efficient tensor network states - a conjecture frequently stated in the context of numerical simulations and analytical considerations. In this talk, I will show that this is in general not the case, except in one dimension. It turns out that the set of quantum many-body states which satisfy an area law for all Renyi entropies contains a subspace of exponential dimension. This implies that there exist area law states which do not have an efficient description in a very general sense, including tensor network states such as polynomial PEPS or MERA. Not even a quantum computer with post-selection can efficiently prepare all quantum states fulfilling an area law, and moreover not all area law states can be eigenstates of local Hamiltonians. I will also discuss variations of these results with translational and rotational invariance as well as decaying correlations. [Based on work with Jens Eisert, arXiv:1411.2995]


04.02.2015 Tba

Guest speaker: Senaida Hernández (ICFO, Spain)

Tba


11.02.2015 Tba

Juan Bermejo-Vega

Tba


18.02.2015 Tba

Guest speaker: Abhiram Kidambi (MPP, Munich)

Tba