Common Origin of Quantum Regression and Quantum Fluctuation Dissipation   Theorems
  It is shown that the quantum fluctuation dissipation theorem can be considered as a mathematical formulation in the spectral representation of Onsager hypothesis on the regression of fluctuations in physical systems. It is shown that the quantum fluctuation dissipation theorem can be generalized to an arbitrary stationary state. 
P. Shiktorov, E. Starikov, V. Gruzinskis, L. Reggiani, L. Varani, J.C.   Vaissiere