Decoherence Free Subspace and entanglement by interaction with a common   squeezed bath
  In this work we find explicitly the decoherence free subspace (DFS) for a two two-level system in a common squeezed vacuum bath. We also find an orthogonal basis for the DFS composed of a symmetrical and an antisymmetrical (under particle permutation) entangled state. For any initial symmetrical state, the master equation has one stationary state which is the symmetrical entangled decoherence free state. In this way, one can generate entanglement via common squeezed bath of the two systems. If the initial state does not have a definite parity, the stationary state depends strongly on the initial conditions of the system and it has a statistical mixture of states which belong to the DFS. We also study the effect of the coupling between the two-level systems on the DFS. 
D.Mundarain, M.Orszag