Fractal fluctuations in quantum mechanics

In quantum open systems, transport coejcients such as crosssections or conductance fluctuate as functions of the relevant parameters. These fluctuations give rise to complicated patterns. An important question is their possible fractality. In this paper we present a historical review of fractal fluctuations in quantum systems and their relation to the properties of their classical counterparts. We discuss the original semiclassical predictions and various numerical and experimental results. Some numerical simulations claim explanations based on pure quantum grounds. We thus report an argument that traces fractality back to the statistical properties of the S -matrix poles. Although full understanding of the reasons for fractal fluctuations might seema secondary problem, it could lead to a deeper comprehension of quantum mechanics and its interplay with classical mechanics.