A control protocol of finite dimensional quantum systems using square   pules
  The control protocols of two types of finite dimensional quantum systems are proposed. The feasibility of each protocol is possible and an arbitrary target state can be achieved from initial state by a constant field. The control parameters which are time periods of interaction between systems and control fields in each cycles are connected with the probability amplitudes of target states via trigonometric functions and can be determined analytically. 
Jianju Tang and H. C. Fu
quant-ph