  Frequent measurements can modify the decay of an unstable quantum state with
respect to the free dynamics given by Fermi's golden rule. In a landmark
article, Nature 405, 546 (2000), Kofman and Kurizki concluded that in quantum
decay processes, acceleration of the decay by frequent measurements, called the
quantum anti-Zeno effect (AZE), appears to be ubiquitous, while its
counterpart, the quantum Zeno effect, is unattainable. However, up to now there
have been no experimental observations of the AZE for atomic radiative decay
(spontaneous emission) in free space. In this work, making use of analytical
results available for hydrogen-like atoms, we find that in free space, only
non-electric-dipolar transitions should present an observable AZE, revealing
that this effect is consequently much less ubiquitous than first predicted. We
then propose an experimental scheme for AZE observation, involving the electric
quadrupole transition between D 5/2 and S 1/2 in the heaviest alkali-earth ions
Ca + and Sr +. The proposed protocol is based on the STIRAP technique which
acts like a dephasing quasi-measurement.
