Robust one-step catalytic machine for high fidelity anticloning and W-state generation in a multiqubit system

We propose a physically realizable machine which can either generate multiparticle W-like states, or implement high-fidelity 1 → M (M = 1, 2, ∞) anticloning of an arbitrary qubit state, in a single step. This universal machine acts as a catalyst in that it is unchanged after either procedure, effectively resetting itself for its next operation. It possesses an inherent immunity to decoherence. Most importantly in terms of practical multiparty quantum communication, the machine's robustness in the presence of decoherence actually increases as the number of qubits M increases.