Abstract
An [[n,k,d]] quantum maximum-distance-separable code maps k source qudits to n coded qudits such that any n-(d-1) coded qudits may recover all source qudits and n = k + 2 (d-1). The entropy of the joint state of the reference system of k qudits and the n coded qudits is fully characterized - the joint state must be pure, i.e., has entropy zero; and any sub-system whose number of qudits is at most half of k+n, the total number of qudits in the joint state must be maximally mixed, i.e., has entropy equal to its size.