Unstable quantum systems are predicted to exhibit a short time deviation from the exponential decay law. This universal phenomenon has led to the prediction that frequent measurements during this nonexponential period could inhibit decay of the system, one form of the quantum Zeno effect. Subsequently, it was predicted that an enhancement of decay due to frequent measurements could be observed under somewhat more general conditions, leading to the so-called anti-Zeno effect.
Depending on the regime of measurement, a suppression or enhancement of the decay rate can be observed. This means depending on the frequency of measurements the decay is suppressed or enhanced.
The key to observing the Zeno and Anti-Zeno effects
is the ability to measure the state of the system in order
to repeatedly redefine a new initial state.