# Geometry of the set of quantum correlations. (arXiv:1710.05892v3 [quant-ph] UPDATED)

It is well known that correlations predicted by quantum mechanics cannot be

explained by any classical (local-realistic) theory. The relative strength of

quantum and classical correlations is usually studied in the context of Bell

inequalities, but this tells us little about the geometry of the quantum set of

correlations. In other words, we do not have good intuition about what the

quantum set actually looks like. In this paper we study the geometry of the

quantum set using standard tools from convex geometry. We find explicit

examples of rather counter-intuitive features in the simplest non-trivial Bell

scenario (two parties, two inputs and two outputs) and illustrate them using

2-dimensional slice plots. We also show that even more complex features appear

in Bell scenarios with more inputs or more parties. Finally, we discuss the

limitations that the geometry of the quantum set imposes on the task of

self-testing.