Time-dependent Decoherence-Free Subspace
  With time-dependent Lindblad operators, an open system may have a time-dependent decoherence-free subspace (t-DFS). In this paper, we define the t-DFS and present a necessary and sufficient condition for the t-DFS. Two examples are presented to illustrate the t-DFS, showing that this t-DFS is not trivial, when the dimension of the t-DFS varies. 
S. L. Wu, L. C. Wang, X. X. Yi
quant-ph