Song, QC; Baker, TJ; Wiseman, HM
Quantum steering is the phenomenon whereby one party (Alice) proves entanglement by “steering” the system of another party (Bob) into distinct ensembles of states, by performing different measurements on her subsystem. Here, we investigate steering in a network scenario involving n parties, who each perform local measurements on part of a global quantum state, that is produced using only two-party entangled states, and mixing with ancillary separable states. We introduce three scenarios which can be straightforwardly implemented in standard quantum optics architecture, which we call random n2-pair entanglement, random pair entanglement, and semirandom pair entanglement. We study steerability of the states across two-party marginals which arise in the three scenarios, and analytically derive the necessary and sufficient steering criteria for different sets of measurement settings. Strikingly, using the semirandom pair entanglement construction, one party can steer every one of the n1 other parties, for arbitrarily large n, using only two measurements. Finally, exploiting symmetry, we study various small network configurations (three or four parties) in the three scenarios, under different measurements and produced by different two-party entangled states.