Laser control of a multilevel quantum system as static parameter optimization with the help of effective decomposition

A quantum control scheme for multilevel systems utilizing effective decomposition is proposed. In this method, a subsystem chosen for control target is effectively isolated by irradiating intense continuous-wave laser fields onto the complimentary space. By choosing the control target space consisting of small number of eigenstates, effective dressed states for the isolated space are analytically given, which makes it possible to express the performance index defined in the target space as an explicit function of laser parameters. Then, designing the control field can be treated as a static parameter optimization. The present scheme makes it possible not only to optimize the laser parameters but also to investigate the parameter search space, which clarifies the physics of the control process.