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Published on Feb 16, 2016
QIP 2016, Banff, 10-16 January 2016
Title: "Noncontextuality violation as a robust quantum resource." Authors: Mike Mazurek, Matthew Pusey*, Ravi Kunjwal, Kevin Resch and Robert Spekkens.
Abstract: Connections between quantum theories violation of formal notions of classicality and its information processing advantages have been studied, shedding new light on both. But since the latter are only relevant to the real world if they are robust to imperfect realisations, it is important for this line of work that the notions of classicality are similarly robust. Local causality meets the condition, but does noncontextuality? This talk will outline our solutions to two apparent failures of robustness for noncontextuality: the first being the apparent requirement of exact operational equivalences between distinct procedures, and the second being that many proofs of contextuality call for measurements that are projective. Both of these are addressed without any change to Spekkens' operational definition of contextuality, instead we rely on better use of the structure of probabilistic theories, in particular convex combinations. This structure turns out to already provide the necessary ``continuity'' to deal with imperfect realizations. The talk will also mention our experimental refutation of noncontextuality that builds on these ideas. Time permitting, the talk will end with some speculation on how these ideas could enable cryptography that doesn't assume all of quantum theory, even in a prepare-and-measure scenario. This highlights that noncontextuality can be applied in scenarios where local causality is simply not relevant.