  Temporal steering is a form of temporal correlation between the initial and
final state of a quantum system. It is a temporal analogue of the famous
Einstein-Podolsky-Rosen (spatial) steering. We demonstrate, by measuring the
photon polarization, that temporal steering allows two parties to verify if
they have been interacting with the same particle, even if they have no
information about what happened with the particle in between the measurements.
This is the first experimental study of temporal steering. We also performed
experimental tests, based on the violation of temporal steering inequalities,
of the security of two quantum key distribution protocols against individual
attacks. Thus, these results can lead to applications for secure quantum
communications and quantum engineering.
