Why do we use the rotating wave picture to make approxiamations in open quantum systems? I understand why we use the Heisenberg picture when switching to the interaction picture. But why rotating picture?
Chris Fleming and his colleges have a nice article about this matter.
As a very short answer I should say that We have two distinct rotating-waveapproximations:
1) The pre-trace RWA is an approximation performed on the interaction Hamiltonian before the en-vironment is traced out which yields a somewhat modified Hamiltonian dynamics from which the reduced dynamics can be derived.
2)The post-trace RWA is performed on the master equation for the reduced density matrix after the environment has already been traced out.
You can also take a look at https://arxiv.org/abs/1401.7350.pdf . They studied the dynamics of a two-level quantum system interact ing with a single frequency electromagnetic field and a stochastic magnetic field, with and without making the rotating wave approximation!