  Entangled neutral K-mesons allow the study of their correlated dynamics at
interference and decoherence times not accessible in any other system. We find
novel quantum phenomena associated to a correlation-in-time between the two
partners: the past state of the first decayed kaon, when it was entangled
before its decay, is post-tagged by the result and the time of the future
observation of the second decay channel. This surprising "from future to past"
effect is fully observable and leads to the unique experimental tag of the
KS-state, an unsolved problem since the discovery of CP violation.
