Revisiting Hardy's paradox: counterfactual statements, real measurements, entanglement and weak values

Hardy's paradox is revisited. Usually the paradox is dismissed on grounds of counterfactuality, i.e., because the paradoxical effects appear only when one considers results of experiments which do not actually take place. We suggest a new set of measurements in connection with Hardy's scheme, and show that when they art! actually performed, they yield strange and surprising outcomes. More generally, we claim that counterfactual paradoxes point to a deeper structure inherent to quantum mechanics. (C) 2002 Published by Elsevier Science B.V.