  We study the ability of a quantum channel to generate quantum coherence when
it applies to incoherent states. Based on probabilistic averages, we define a
measure of such coherence generating power (CGP) for a generic quantum channel,
based on the average coherence generated by the quantum channel acting on a
uniform ensemble of incoherent states. Explicit analytical formula of the CGP
for any unitary channels are presented in terms of subentropy. An upper bound
for CGP of unital quantum channels has been also derived. Detailed examples are
investigated.
