An open-source linear program for testing nonclassicality

Anomalous weak values require coherence

“…This could be done using recently proposed quantum circuits that measure weak values [12,14]. We also remark on the relevance of recently established connections between unitary invariants and contextuality [15], together with techniques for testing contextuality without relying on operational constraints [16][17][18]. These results enable us here to present simple ways to robustly quantify contextuality using measurements of weak values, allowing novel simplified tests of contextuality.…”

“…If g(φ, ψ|a i ) > 1 holds, then letting S = {|φ , |ψ , |a 1 , |a 2 , |φ ⊥ , |ψ ⊥ }, where |φ ⊥ is the antipodal state of |φ in the Bloch sphere, and effects E = S, then it can be shown that the fragment (S, E) cannot have a noncontextual explanation. To robustly test this, one can use linear programming techniques that will indicate presence of contextuality directly, and moreover return robustness to depolarizing [18] and dephasing noise [52]. The case for d > 2, or anomalous imaginary values of g are not so direct but can also be analysed with the tools discussed here.…”

Accessible fragments of generalized probabilistic theories, cone equivalence, and applications to witnessing nonclassicality

“…Furthermore, the proof does not actually use the full geometric structure of accessible GPT fragments but only that of a "GPT fragment," see Ref [104]…”