Remarks about Bell-nonclassicality of a single photon

We discuss the interferometric scheme put forward by Tan, Walls, and Collett (TWC) that claims to reveal Bell non-classicality of a single photon. We show that the violation of local realism they report hinges on an additional assumption about hidden variables. Without it, one can construct a classical model that correctly predicts all the probabilities of the TWC scheme. To illustrate this, we construct a proper Bell inequality, devoid of additional assumptions, that is not violated by the TWC setup. We then show a modification of the interferometric scheme, consisting in making the amplitude of auxiliary fields tunable, that enables the Bell violation. Finally, we present an alternative point of view on the shortcomings of the original TWC analysis, arguing that it effectively treats the weak coherent states classically. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this article, we discuss the interferometric scheme proposed by Tan, Walls, and Collett (TWC) that claims to reveal the Bell non-classicality of a single photon. We demonstrate that the violation of local realism reported by TWC relies on an additional assumption about hidden variables. Without this assumption, it is possible to construct a classical model that accurately predicts all the probabilities of the TWC scheme. We present a proper Bell inequality that does not require additional assumptions and is not violated by the TWC setup. Additionally, we propose a modification of the interferometric scheme by making the amplitude of auxiliary fields tunable, which enables Bell violation. Finally, we provide an alternative perspective on the shortcomings of the original TWC analysis, arguing that it treats weak coherent states as classical.