Efficient Multi‐Stage Entanglement Distillation for W States

ABSTRACT W states are essential resources in quantum communication and computation but are highly vulnerable to decoherence. We propose a three‐stage, non‐recursive entanglement distillation protocol that extracts a maximally entangled W state from multiple copies of amplitude‐damped W states, applicable to both the standard and generalized W states. Unlike conventional recursive schemes, the proposed protocol imposes no constraints on the initial fidelity of the input states and achieves unit‐fidelity distillation with improved efficiency and success probability. Instead of iteratively enhancing entanglement fidelity, our approach constructs a specific non‐trivial sacrificial‐state structure within the first two stages of the protocol. By sacrificing this intermediate state in the final stage, the protocol enables the distillation of a maximally entangled W state from an amplitude‐damped input, offering a new non‐recursive route to high‐fidelity multipartite entanglement purification. Comparative analysis demonstrates that the proposed method significantly outperforms the weak‐measurement‐based distillation protocol across all decay rates. The IBM Qiskit simulations further validate the analytical predictions, confirming both the correctness and the practical feasibility of the proposed protocol.