  We solve a model of a qubit strongly coupled to a massive environmental
oscillator mode where the qubit backaction is treated exactly. Using a
Ginzburg-Landau formalism, we derive an effective action for this well known
localization transition. An entangled state emerges as an instanton in the
collective qubit-environment degree of freedom and the resulting model is shown
to be formally equivalent to a Fluctuating Gap Model (FGM) of a disordered
Peierls chain. Below the transition, spectral weight is transferred to an
exponentially small energy scale leaving the qubit coherent but damped. Unlike
the spin-boson model, coherent and effectively localized behaviors may coexist.
