  The quantum Zeno effect is the prediction, going back to Alan Turing, that
the decay of an unstable system can be slowed down by measuring it frequently
enough. It was also noticed later that the opposite effect, i.e., enhancement
of the decay due to frequent measurements, is rather common. An important
question arising in this regards is how to choose the optimal measurement
strategy to achieve the highest possible decay rate. Here we rigorously prove
the universal optimality of the stroboscopic measurement protocol in the sense
that it always provides the shortest expected decay time among all measurement
procedures. However, the implementation of the stroboscopic protocol requires
the knowledge of the optimal sampling period which may depend on the fine
details of the quantum problem. We show that this difficulty can be overcame
with the simple non-regular measurement procedures inspired by the scale-free
restart strategies used to speed up the completion of random search tasks and
probabilistic algorithms in computer science. Besides, our analysis reveals the
universal criteria to discriminate between Zeno and anti-Zeno regimes for the
unstable quantum systems under Poissonian measurements.
