Theory Seminar
From MPQTheory

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 wellknown LeggettGarg inequalitites. In this talk I will discuss a condition called nosignaling 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 manybody states
Yimin Ge It is commonly believed that area laws for entanglement entropies imply that a quantum manybody 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 manybody 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 postselection 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 BermejoVega Tba

18.02.2015  Tba
Guest speaker: Abhiram Kidambi (MPP, Munich) Tba 