Fluctuation-dissipation theorem and quantum tunneling with dissipation

We suggest to take the fluctuation-dissipation theorem of Callen and Welton as a basis to study quantum dissipative phenomena ( such as macroscopic quantum tunneling ) in a manner analogous to the Nambu-Goldstone theorem for spontaneous symmetry breakdown. It is shown that the essential physical contents of the Caldeira-Leggett model such as the suppression of quantum coherence by Ohmic dissipation are derived from general principles only, namely, the fluctuationdissipation theorem and unitarity and causality (i.e., dispersion relations), without referring to an explicit form of the Lagrangian. An interesting connection between quantum tunneling with Ohmic dissipation and the Anderson’s orthogonality theorem is also noted. 1 Fluctuation-dissipation theorem The quantum dissipative phenomena[1] are related to the study of irreversible processes in quantum statistical mechanics, and as such they have been studied by many authors in the past, in particular, in the framework of linear response theory[2][3]. A combination of dissipation with quantum tunneling adds further interesting aspects to the subject and potentially covers a wide class of phenomena in various fields of physics. In the analysis of macroscopic quantum tunneling with dissipation, the model defined by Caldeira and Leggett[4] is widely used. One of the essential ingredients of their model