Ericson fluctuations

Ericson fluctuations constitute one of the most characteristic features of quantum chaotic scattering in the regime of strongly overlapping resonances such as a compound nucleus.^[1][2][3] These fluctuations were predicted in 1960 by Torleif Ericson in two seminal articles,^[4][5][6][7] further developed in 1963,^[8] based on the same statistical assumptions as those used by E. Wigner, C. E. Porter and R. G. Thomas to describe generic properties of resonances in long-lived compound nuclear systems.^[9][10][11] In the present case the fluctuations occur in the "continuum" regime for which a large number of such resonances overlap coherently, owing to the short lifetime of the compound nucleus. At the time it was believed that this would lead to a structure-less behavior. Ericson realized that the opposite was the case with strong, random fluctuations.^[12][7]

The Ericson fluctuations were first observed in 1964 by P. Von Brentano et al.^[13] in nuclear physics giving rise to a vigorous theoretical and experimental programme.^[3] They have the curious feature of being both reproducible and random at the same time.^[14] The fluctuations are universal and have later been observed in many other areas such as photoionization of hydrogen, uni-molecular dissociation (physical chemistry),^[15] perturbed atomic and molecular systems and micro wave billiards.^[3][16][17]

Present theoretical descriptions of chaotic quantum scattering confirm the predicted properties of the Ericson fluctuations.^[9] The universality of the Ericson fluctuations are thus very well established.^[3]