Observation of the quantum Zeno and anti-Zeno effects in an unstable system - art. no. 040402

We report the first observation of the quantum Zeno and anti-Zeno effects i n an unstable system. Cold sodium atoms are trapped in a far-detuned standi ng wave of light that is accelerated for a controlled duration. For a large acceleration the atoms can escape the trapping potential via tunneling. In itially the number of trapped atoms shows strong nonexponential decay featu res, evolving into the characteristic exponential decay behavior. We repeat edly measure the number of atoms remaining trapped during the initial perio d of nonexponential decay. Depending on the frequency of measurements we ob serve a decay that is suppressed or enhanced as compared to the unperturbed system.