Distributed Cloning Cuts Entanglement Fidelity by [c] to the Nth Power

Researchers Pritam Roy, William John Munro, and Shashank Gupta have established operational limits on the broadcasting of genuine multipartite entanglement (GME) in quantum networks. Their work establishes that fidelity decays exponentially with system size as c to the Nth power, providing a quantitative expression of multipartite entanglement monogamy in the broadcasting setting, and that both state families share a universal normalisation factor arising from independent post-selection probabilities. Most significantly, the team proved a no-go result for simultaneous GME certification: for all reflectivities and all system sizes, the two broadcast copies cannot be simultaneously certified as genuinely multipartite entangled within the standard framework of fidelity-based witnesses. The results reveal a trade-off between broadcasting entanglement…