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"Steered towards non-locality
Quantum mechanics predicts that measurements on spatially separated particles can yield non-local correlations.
This is well established but defies intuition about space and time. The concept of ‘steering’ might help us to
understand quantum non-locality better. ... Dylan Saunders et al.1 propose a fresh view on quantum non-locality by investigating the little-explored concept of ‘steering’. ... They devise simple ‘steering inequalities’ — analogous to Bell inequalities3 — that allow Bob to determine whether or not steering occurred. ... In their experiments, Saunders et al.1 generate pairs of polarization-entangled photons that can subsequently be depolarized very accurately. By adding exactly the right amount of noise, they prepare the photon pairs in entangled states that are ‘Bell local’ 8,9, meaning that the pairs cannot violate any Bell inequality. Then they demonstrate that these states are nevertheless steerable, by demonstrating a clear violation of the steering inequalities.

Figure 1 | Three fundamentally different forms of quantum non-locality.

a, To test for entanglement, trusted devices (white boxes) are used, which are supposed to obey the laws of quantum mechanics.

b, Non-locality is defined independently of quantum mechanics, however, and can be tested without any prior knowledge about the devices (black boxes).

c, Steering is intermediate: one party trusts only its own measuring device, but not the other party."

Nicolas Brunner