Explicit formula for the external driving field used to eliminate the   decoherence of a two-state system coupled to a noise field
  The elimination of decoherence of a multiphoton two-state quantum system by using an appropriate external driving field is considered. The multiphoton process caused by the noise field has a supersymmetric Lie algebraic structure. The time-evolution equations for the off-diagonal elements of the density operator of the two-state system are derived in the interaction picture. A simple explicit formula is given for the time-dependent external driving field used to eliminate the decoherence of the multiphoton two-state system. 
Jian-Qi Shen, Zhi-Chao Ruan, and Sailing He