The concept of ‘steering’ was introduced in 1935 by Schrödinger1 as a generalization of the EPR (Einstein–Podolsky–Rosen) paradox. It has recently been formalized as a quantum-information task with arbitrary bipartite states and measurements2, for which the existence of entanglement is necessary but not sufficient. Previous experiments in this area3, 4, 5, 6 have been restricted to an approach7 that followed the original EPR argument in considering only two different measurement settings per side. Here we demonstrate experimentally that EPR-steering occurs for mixed entangled states that are Bell local (that is, that cannot possibly demonstrate Bell non-locality). Unlike the case of Bell inequalities8, 9, 10, 11, increasing the number of measurement settings beyond two—we use up to six—significantly increases the robustness of the EPR-steering phenomenon to noise.
At a glance
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