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 a 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 is a statistical mixture of states which belong to DFS. We also study the effect of the coupling between the two-level systems on the DFS.