Perspectives on 1/f noise in quantum chaos

The power spectrum of the ?n statistic of quantum spectra presents 1/f? noise. For chaotic systems ? = 1 while for regular systems ? = 2. Although the transition from regularity to chaos is non universal, for a wide variety of systems with a mixed phase space the value of ? is intermediate between 1 and 2 and can be related to the fraction of regular or chaotic orbits in the total phase space. This statistic can be a very useful tool for the analysis of experimental spectra, specially in the case of missing levels or spectral sequences with mixed symmetries.