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Amending coherence-breaking channels via unitary operations
Long-Mei Yang, Bin Chen, Shao-Ming Fei and Zhi-Xi Wang
The coherence-breaking channels play a significant role in quantum information theory. We study the coherence-breaking channels for qubit systems and give a method to amend the coherence-breaking channels by applying unitary operations. For given incoherent channel $\Phi$, we give a necessary and sufficient condition for the channel to be a coherence-breaking channel and amend it via unitary operations. For incoherent channels $\Phi$ that are not coherence-breaking ones, we consider $\Phi\circ\Phi$ and give the conditions for coherence-breaking and channel amendment as well.