  We propose a characterisation of the effects of bistable coherent impurities
in solid state qubits. We introduce an effective impurity description in terms
of a tunable spin-boson environment and solve the dynamics for the qubit
coherences. The dominant rate characterizing the asymptotic time limit is
identified and signatures of non-Gaussian behavior of the quantum impurity at
intermediate times are pointed out. An alternative perspective considering the
qubit as a measurement device for the spin-boson impurity is proposed.
