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arXiv:0802.0472 · Physical Review A

Possible entanglement detection with the naked eye

Nicolas Brunner, Cyril Branciard, Nicolas Gisin

Published Nov 12, 2008• 32 citations

Abstract

The human eye can detect optical signals containing only a few photons. We investigate the possibility to demonstrate entanglement with such biological detectors. While one person could not detect entanglement by simply observing photons, we discuss the possibility for several observers to demonstrate entanglement in a Bell-type experiment, in which standard detectors are replaced by human eyes. Using a toy model for biological detectors that captures their main characteristic, namely, a detection threshold, we show that Bell inequalities can be violated, thus demonstrating entanglement. Remarkably, when the response function of the detector is close to a step function, quantum nonlocality can be demonstrated without any further assumptions. For smoother response functions, as for the human eye, postselection is required.

DOI: 10.1103/physreva.78.052110

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Progress in multiphoton interferometry allows us now to observe even six-photon interference of a very high contrast. Also, it is possible to observe interference of two photons originating from truly independent sources. Non-classical effects may violate Bell inequalities, or reveal quantum non-separability. Methods of producing non-classical states of few photons, and the detection of entanglement via Bell inequalities, or via nor-separability criteria will be presented. Implications of violations of Bell inequalities will be discussed, with a special stress on over-interpretations of this fact.