Frequent observations accelerate decay: The anti-Zeno effect

The quantum Zeno effect (QZE) is the striking prediction that the decay of any unstable quantum state can be inhibited by sufficiently frequent observ ations (measurements). The consensus opinion has upheld the QZE as a genera l feature of quantum mechanics which should lead to the inhibition of any d ecay. The claim of QZE generality hinges on the assumption that successive observations can in principle be made at time intervals too short for the s ystem to change appreciably. However, this assumption and the generality of the QZE have scarcely been investigated thus far. We have addressed these issues by showing that (i) the QZE is principally unattainable in radiative or radioactive decay, because the required measurement rates would cause t he system to disintegrate; (ii) decay acceleration by frequent measurements (the anti-Zeno effect - AZE) is much more ubiquitous than its inhibition. The AZE is shown to be observable as the enhancement of tunneling rates (e. g., for atoms trapped in ramped-up potentials or in current-swept Josephso n junctions), fluorescence rates (e. g., for Rydberg atoms perturbed by noi sy optical fields) and photon depolarization rates (in randomly modulated P ockels cells).