The lifetime of an unstable atom can be extended by watching it closely, i.e., illuminating it with an intense electromagnetic field of appropriate frequency. This is an example of “dominated evolution” and is closely related to the so-called “quantum Zeno effect.” For a metastable atom bathed in a laser beam at the frequency of another of its transitions, we obtain an expression for the modified lifetime as a function of beam intensity. This provides an example of the quantum Zeno effect on a truly decaying system, and also should be useful for probing short distance features of atomic wave functions.

• Received 31 July 1996

DOI:https://doi.org/10.1103/PhysRevA.56.25