Intermittent search strategies:: When losing time becomes efficient

In this letter, we show that intermittent search strategies, alternating active search phases and non-reactive displacement phases, are universal for a wide class of problems involving search time optimization. More precisely, we address the general question of determining in which cases a searcher should, or should not, interrupt his search activity by "losing" time in non-reactive phases of mere displacement, and which durations of each phase optimize the search time. Using a representative analytical model, we show that intermittent strategies do optimize the search time as soon as the target is "difficult" to detect, and we explicitly give the optimal search strategies, which depend on the memory skills of the searcher.