The Meaning of the Interaction-Free Measurements

Interaction-free measurements introduced by Elitzur and Vaidman Found. Phys. 23, 987 (1993)] allow finding infinitely fragile objects without destroying them. Many experiments have been successfully performed showing that indeed, the original scheme and its modifications lead to reduction of the disturbance of the observed systems. However, there is a controversy about the validity of the term interaction-free for these experiments. Broad variety of such experiments are reviewed and the meaning of the interaction-free measurements is clarified.