Universal and phase-covariant superbroadcasting for mixed qubit states
Francesco Buscemi, Giacomo Mauro D’Ariano, Chiara Macchiavello, Paolo Perinotti · Physical Review A · 2006
We describe a general framework to study covariant symmetric broadcasting maps for mixed qubit states. We explicitly derive the optimal $N\ensuremath{\rightarrow}M$ superbroadcasting maps, achieving optimal purification of the single-site output copy, in both the universal and phase-covariant cases. We also study the bipartite entanglement properties of the superbroadcast states.