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, refined in a seminal article in 1963,[4][5][6] 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.[7][8][9] 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.[10][11]

The Ericson fluctuations were first observed in 1964 by P. Von Brentano et al. in compound nuclear reactions.[12] They have the curious feature of being both reproducible and random at the same time.[13] The fluctuations are universal and have later been observed in many other areas such as photoionization of hydrogen, uni-molecular dissociation (physical chemistry),[14] perturbed atomic and molecular systems and micro wave billiards.[3][15][16]

Present theoretical descriptions of chaotic quantum scattering confirm the predicted properties of the Ericson fluctuations.[7] The universality of the Ericson fluctuations are thus very well established.[3]