- We assume that the energy spectrum of the bath of oscillators is spaced tightly enough relative to its overall domain, i.e. such that the approximation , where is the density of states of the reservoir, is a physically acceptable mathematical assumption.
- Related to the previous assumption, we assume that the bath is large enough and in a state of equilibrium such that any perturbations caused by the individual system on the bath is negligible. This is to say, the future state of the system-bath density operator is determined by its current state, and is not a function of the history of the bath (that is, we assume ).This is the Markoffian assumption.
- We assume the rotating wave approximation regime. The interaction of the bath and system will have terms such as . The lowering-lowering and raising-raising coupling has a much slower varying contribution to the state of the system, and so are excluded to give the interaction Hamiltonian where is a real coupling constant. Obviously, one must be certain the system one models can be simplified as such in order to apply the general master equation.