Postquantum steering in bipartite scenarios

In a traditional bipartite steering experiment, the assemblages (ensembles of ensembles) into which Alice remotely steers Bob’s system may always be explained via quantum mechanics. This is a renowned result by Gisin, Hughston, Jozsa and Wootters. Here we answer the question of whether steering that is not compatible with quantum theory may still arise in bipartite scenarios for a suitable relaxation of the experimental setup. We find that, on the one hand, scenarios where Alice steers Bob’s system via a sequence of measurements on her share of the system, are always compatible with quantum theory. On the other hand, in scenarios where Bob is now allowed to also act on his share of the system via some transformation, assemblages with no quantum explanation may arise.