Observation of the Quantum Zeno and Anti-Zeno Effects in AN Unstable System

We report the first observation of the Quantum Zeno effect (QZE) and Anti-Zeno effect (AZE) in an unstable system. These effects are the inhibition or enhancement of decay by frequent measurement during the non-exponential time. The experiment builds on our earlier observation of short-time deviations from exponential decay in the tunneling of atoms from accelerating lattices. Recent improvements in the experiment and development of the measurement method have now allowed us to observe both the QZE and the AZE.