Completely positive approximate solutions of driven open quantum systems
  We define a perturbative approximation for the solution of Lindblad master equations with time-dependent generators that satisfies the fundamental property of complete positivity, as essential for quantum simulations and optimal control. With explicit examples we show that ensuring this property substantially improves the accuracy of the perturbative approximation. 
Farhang Haddadfarshi, Jian cui, Florian Mintert
quant-ph cond-mat.other