Loophole-free Quantum Steering

Experiments testing quantum mechanics have provided increasing evidence against local realistic theories. However, a conclusive test that simultaneously closes all major loopholes (the locality, freedom-of-choice, and detection loopholes) remains an open challenge. An important class of local realistic theories can be tested with the concept of ``steering.'' Schr\"{o}dinger introduced this term for entanglement seemingly allowing to remotely steer the state of a distant system [1]. Einstein called this ``spooky action at a distance.'' Steering was recently formalized by deriving steering inequalities allowing experimental tests. Here, we present the first loophole-free steering experiment [2]. We use entangled photons shared between two distant laboratories and close all loopholes by a large separation, ultra-fast switching and quantum random number generation, and high, overall detection efficiency. Beside its foundational importance loop-hole-free steering is relevant for is relevant for device-independent certification of quantum entanglement. \\[4pt] [1] E. Schr\"{o}dinger, Proc. Camb. , Phil. Soc. 31, 553 (1935) \\[0pt] [2] B. Wittmann, S. Ramelow, F. Steinlechner, N. K. Langford, N. Brunner, H. Wiseman, R. Ursin, A. Zeilinger, arXiv:1111.0760, (2011)