Re: [Aspuru-Guzik group list] [qip] Friday

Also, after the meeting will be a talk by Adam Bouland. ------- Adam Bouland will be speaking at the CTP Graduate Lunch Club on Friday. When: 12:00 pm, Friday 22 March. Where: Cosman Seminar Room, 6C-442. Speaker: Adam Bouland (from CSAIL) Title: Psi-Epistemic Theories: The Role of Symmetry (based on http://arxiv.org/abs/1303.2834) Abstract: Formalizing an old desire of Einstein, "psi-epistemic theories" try to reproduce the predictions of quantum mechanics, while viewing quantum states as ordinary probability distributions over underlying objects called "ontic states." Regardless of one's philosophical views about such theories, the question arises of whether one can cleanly rule them out, by proving no-go theorems analogous to the Bell Inequality. In the 1960s, Kochen and Specker (who first studied these theories) constructed an elegant psi-epistemic theory for Hilbert space dimension d=2, but also showed that any deterministic psi-epistemic theory must be "measurement contextual" in dimensions 3 and higher. Last year, the topic attracted renewed attention, when Pusey, Barrett, and Rudolph (PBR) showed that any psi-epistemic theory must "behave badly under tensor product." In this paper, we prove that even without the Kochen-Specker or PBR assumptions, there are no psi-epistemic theories in dimensions d>=3 that satisfy two reasonable conditions: (1) symmetry under unitary transformations, and (2) "maximum nontriviality" (meaning that the probability distributions corresponding to any two non-orthogonal states overlap). On the other hand, we also show the surprising result that without the symmetry restriction, one can construct maximally-nontrivial psi-epistemic theories in every finite dimension d. ------ On Thu, Mar 21, 2013 at 3:07 PM, Edward Farhi <farhi(a)mit.edu> wrote: _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip