Quandela, France, shane.mansfield@quandela.com
(joint work with Boris Bourdoncle, Pierre-Emmanuel Emeriau, Damian Markham, Andreas Fyrillas, Boris Bourdoncle, Alexandre Mainos, Kayleigh Start, Pierre-Emmanuel Emeriau, Nico Margaria, Martina Morassi, Aristide Lemaitre, Isabelle Sagnes, Petr Stepanov, Thi Huong Au, Sebastien Boissier, Niccolo Somaschi, Nicolas Maring, Nadia Belabas)
Contextuality is often defined in terms of hidden variables, for which it forces a contradiction with the assumptions of parameter-independence and determinism. The former can be justified by the empirical property of non-signalling or non-disturbance, and the latter by the empirical property of measurement sharpness. However in realistic experiments neither empirical property holds exactly, which leads to possible objections to accepting contextuality as a form of nonclassicality, which we will refer to as the compatibility and sharpness loopholes. The compatibility loophole is especially problematic for contextuality experiments which do not enforce spacelike separation between devices. Moreover, these introduce knock-on vulnerabilities for supposed quantum advantages that rely on contextuality. In Part 1 of this talk we introduce measures to quantify both properties, and introduce quantified relaxations of the corresponding assumptions. We prove a continuity result on the contextual fraction measure of contextuality to ensure its robustness to noise. We then bound the extent to which these relaxations can account for contextuality, via corrections terms to the contextual fraction (or to any noncontextuality inequality), culminating in a notion of genuine contextuality, which is robust to experimental imperfections. In Part 2 of the talk we describe an integrated photonic demonstration with an effective 2-qubit device combining a solid-state emitter and a glass chip. We neither have nor suppose spacelike separation, and instead account for information leakage to address the compatibility loophole and witness genuine contextuality. The method is thus suitable for upcoming compact scalable devices. We finally discuss the prospect of using the approach to achieve quantum advantage in practical applications.