When Quantum Channel Preserves Product States.

Product states are always considered as the states that do not contain quantum correlation. We discuss here when a quantum channel sends the product states to themselves. Exact forms of such channels are proposed. It is shown that such a quantum channel is a local quantum channel, a composition of a local quantum channel and a flip operation, or such that one of the local states is fixed. Both finite- and infinite-dimensional systems are considered. [ABSTRACT FROM AUTHOR]