Optimal control of multilevel quantum systems in the field-interaction representation

A control strategy incorporating a fixed carrier frequency constraint on the optimal field is presented. As an illustrative example we consider the creation of maximum coherence in a six-level Λ system by solving the Schrödinger equation without the rotating-wave approximation in the field-interaction representation. We demonstrate that application of the optimal control theory optimization reformulated in the field-interaction representation allows one to keep the carrier frequency of the control field constant and successfully optimize off-resonant processes in multilevel quantum systems.