  We study the relationship between one-dimensional fermion gas-impurity models
and quantum dissipative systems, via the method of constructive bosonisation
and unitary transformation. Starting from an anisotropic Coqblin-Schrieffer
model, a new, exactly solvable, three-level quantum dissipative system is
derived as a generalisation of the standard spin-half spin-boson model. The new
system has two environmental oscillator baths with ohmic coupling, and admits
arbitrary detuning between the three levels. All tunnelling matrix elements are
equal, up to one complex phase which is itself a function of the longitudinal
and transverse couplings in the integrable limit. Our work underlines the
importance of re-examining the detailed structure of fermion-gas impurity
models and spin chains, in the light of connections to models for quantum
dissipative systems.
