Non-classicality of temporal correlations

Understand

The results of space-like separated measurements are independent of distant measurement settings, a property one might call two-way no-signalling.

• In contrast, time-like separated measurements are only one-way no-signalling since the past is independent of the future but not vice-versa.
• For this reason temporal correlations that are formally identical to non-classical spatial correlations can still be modelled classically.
• We define non-classical temporal correlations as the ones which cannot be simulated by propagating in time a classical information content of a quantum system.