1202.3449 (M. E. Shirokov)

A simple criterion for coincidence of the entanglement-assisted
classical capacity and the Holevo capacity of a quantum channel    [PDF]

M. E. Shirokov

It is easy to show coincidence of the entanglement-assisted classical
capacity and the Holevo capacity for any c-q channel. In this brief note we
prove the converse assertion: coincidence of the above-mentioned capacities of
a quantum channel implies that the $\chi$-essential part of this channel is a
c-q channel (the $\chi$-essential part is a restriction of a channel obtained
by discarding all input states useless for transmission of classical
information).

View original: http://arxiv.org/abs/1202.3449