Decoherence-free subspaces and incoherently generated coherences

A decoherence-free subspace (DFS) is a collection of states that is immune to the dominant noise effects created by the environment. DFS is usually studied for states involving two or more particles and is considered a prominent candidate for quantum memory and quantum information processing. We present rigorous criteria for the existence of DFS in finite-dimensional systems coupled to the Markovian reservoirs. This allows us to identify a new special class of decoherence free states that relies on rather counterintuitive phenomenon, which we call an ``incoherent generation of coherences.'' We provide examples of physical systems that support such states.