Quantum state fusion via generalized measurement

Abstract

Large-scale entangled states are important physical resources, which can be generated from small-scale ones via quantum state fusion. Measurement in fusion operation will cause particle and efficiency loss, so a fusion scheme without qubit loss is expected to be the most efficient one, but counter-intuitively it is not the case. So in this paper we reveal the essence of the fusion mechanism, and answer this counter-intuitive question. The results show that any fusion mechanism is basically a generalized measurement (POVM), and the POVM essence shows why the qubit-loss-free fusion scheme for standard W state is not the most efficient one. A more efficient fusion mechanism targeting at large-scale W state is proposed, where two unequally-weighted W states are fed into the fusion mechanism, and it beats all the current fusion schemes. The universality of the POVM essence of the fusion mechanism makes it applicable to any multipartite entangled state.