Perturbative Treatment of the Evolution Operator Associated with Raman   Couplings
  A novel perturbative treatment of the time evolution operator of a quantum system is applied to the model describing a Raman-driven trapped ion in order to obtain a suitable 'effective model'. It is shown that the associated effective Hamiltonian describes the system dynamics up to a certain transformation which may be interpreted as a 'dynamical dressing' of the effective model. 
Benedetto Militello, Paolo Aniello and Antonino Messina