Bell polytopes with nontrivial symmetries - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-20T08:31:50Z http://mathoverflow.net/feeds/question/61234 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/61234/bell-polytopes-with-nontrivial-symmetries Bell polytopes with nontrivial symmetries Marcin Kotowski 2011-04-10T18:19:40Z 2011-04-10T18:19:40Z <p>Take $N$ parties, each of which receives an input $s_i \in {1, \dots, m_i}$ and produces an output $r_i \in {1, \dots, r_i}$, possibly in a nondeterministic manner. We are interested in joint conditional probabilities of the form $p(r_1r_2\dots r_N|s_1s_2\dots s_N)$. Bell polytope is the polytope spanned by the probability distributions of the form $p(r_1r_2\dots r_N|s_1s_2\dots s_N) = \delta_{r_1, r_{1, s_1}}\dots\delta_{r_N, r_{N, s_N}}$ for all possible choices of numbers $r_{i,s_i}$ (in other words, each input $s_i$ produces a result $r_{i,s_i}$ either with probability 0 or 1, regardless of other players' inputs). Polytopes of this kind are of interest in quantum information theory.</p> <p>Every Bell polytope has a certain amount of trivial symmetries, like permutation of parties or relabelling of inputs or outputs. Is it possible to give an explicit Bell polytope with nontrivial symmetries? (e.g. transformations of the polytope into itself that takes faces to faces and is not trivial in the above sense)</p> <p>Bell polytopes in literature are usually characterized by their faces, given by sets of inequalities (Bell inequalities), which, however, usually do not have any manifest symmetry group. </p>