  Understanding decoherence processes is crucial in the study of open quantum
systems. In this paper, we discuss the mechanism of pure-dephasing process with
a newly proposed boson-boson model, namely, a bosonic field coupled to another
bosonic bath in thermal equilibrium. Our model is fully solvable and can
reproduce the pure-dephasing process which is usually described by the
well-known spin-boson model, therefore offering a new perspective to
understanding decoherence processes in open quantum systems of high dimension.
We also show that this model admits a generically non-Markovian dynamics with
respect to various different non-Markovian measures.
