= Holevo capacity
{c}
{title2=$\chi^*(\Lambda)$}
= Product-state classical capacity
{synonym}
The Holevo capacity of a <quantum channel> is the maximum one-use output <Holevo quantity>,
$$
\chi^*(\Lambda)=\max_{\{p_x,\rho_x\}}
\left[S\left(\sum_xp_x\Lambda(\rho_x)\right)-\sum_xp_xS(\Lambda(\rho_x))\right].
$$
It is the unassisted classical communication limit for <product state> encodings with collective output measurements. Arbitrary entangled inputs require the regularized expression in the <Holevo-Schumacher-Westmoreland theorem>.
Back to article page
