1/f noise and quantum criticality

One of those nice if obvious-after-the-fact results -- quantum critical correlations are preserved under the addition of 1/f noise. It's obvious after the fact because (a) 1/f noise has power law correlations in time, so it's "critical" in some sense; (b) more precisely, the 1/f noise term appears in the Keldysh action in precisely the same way as the "equilibrium" noise term -- from the FDT -- that drives the superconductor-insulator transition in a Josephson junction.

Quantum critical states and phase transitions in the presence of non-equilibrium noise
E. della Torre et al., Nature Physics doi:10.1038/nphys1754 [also arXiv:0908.0868]