Abstract

The quantum Zeno effect (QZE) is the striking prediction that the decay of any unstable quantum state can be inhibited by sufficiently frequent observations (measurements). The QZE has only been tested and analysed for two coupled states. Yet the consensus opinion upholds the QZE as a general feature of quantum mechanics which should lead to the inhibition of any decay. The claim of QZE generality hinges on the assumption that successive observations can in principle be made at time intervals too short for the system 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 the modification of decay by frequent measurements is determined by the energy spread they incur (in accordance with the time-energy uncertainty relation) and the reservoir to which the decaying state is coupled. Our analysis implies that (i) the QZE is principally unattainable in radiative or radioactive decay, because the required measurement rates would cause the 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 (for atoms trapped in ramped-up potentials current swept Josephson junctions), fluorescence rates (for Rydberg atoms perturbed by noisy optical fields) and photon depolarization rates (in randomly modulated Pockels cells).

© 2000 IEEE