Multi-time entanglement

• Post by: admin
• August 24, 2018
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Entanglement usually refers to stronger-than-classical correlations between spatially separated quantum systems. It can however also manifest itself across points in time, in a number of different ways, as discussed in this excellent popular science article by George Musser.

Most research on temporal correlations goes back to Leggett and Garg, who showed that subsequent measurements on macroscopic quantum systems can reveal temporal correlations that cannot be explained by assuming macro-realism and non-invasive measurements (in analogy to the more commonly known realism and locality in Bell inequalities). It was later shown that temporal correlations can be generalised to direct analogies of e.g. the CHSH inequality, or Hardy’s paradox, and we demonstrated both phenomena in a photonic experiment in 2011.

A lot more work has been done on temporal correlations since, and of particular interest are attempts to use the known mapping between temporal and spatial correlations to unify phenomena such as nonlocality and quantum (non)-contextuality. What was missing though was a general framework for describing temporal correlations that extend beyond simple two-time measurements, and a unified description that allows for the analysis of arbitrary spatio-temporal scenarios.

We address this gap in two new publications, first a primarily theoretical paper, Phys. Rev. A 98, 012328 (2018), that describes precisely such a framework, and shows the simplest case of a spatio-temporal inequality experimentally; and second, an experiment in which we construct and demonstrate multi-time entanglement, npj Quantum Information 4, 37 (2018).