Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Inability of the entropy vector method to certify nonclassicality in
  linelike causal structures   Bell's theorem shows that our intuitive understanding of causation must be
overturned in light of quantum correlations. Nevertheless, quantum mechanics
does not permit signalling and hence a notion of cause remains. Understanding
this notion is not only important at a fundamental level, but also for
technological applications such as key distribution and randomness expansion.
It has recently been shown that a useful way to decide which classical causal
structures could give rise to a given set of correlations is to use entropy
vectors. These are vectors whose components are the entropies of all subsets of
the observed variables in the causal structure. The entropy vector method
employs causal relationships among the variables to restrict the set of
possible entropy vectors. Here, we consider whether the same approach can lead
to useful certificates of non-classicality within a given causal structure.
Surprisingly, we find that for a family of causal structures that include the
usual bipartite Bell structure they do not. For all members of this family, no
function of the entropies of the observed variables gives such a certificate,
in spite of the existence of nonclassical correlations. It is therefore
necessary to look beyond entropy vectors to understand cause from a quantum
perspective.

17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
11
The categories of this paper are: hep-lat
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys