= Additivity of Holevo capacity
{title2=$\chi^*(\Lambda\otimes\Gamma)=\chi^*(\Lambda)+\chi^*(\Gamma)$}
A channel's <Holevo capacity> is additive with another channel when their joint capacity equals the sum of the individual capacities. If this holds with every other channel, the channel's tensor powers have capacity $n\chi^*(\Lambda)$ and regularization does not increase its unassisted <classical capacity of a quantum channel>. Additivity is a special property, not a general rule for quantum channels.
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