Experimental Bell violations with classical, non-entangled optical fields

Abstract

We report experiments in which the Bell parameter S that enters the Clauser-Horne-Shimony-Holt inequality:. In our experiments, we used two spatially separated optical beams, the electric fields of which were correlated to one another. The amount of correlation was quantified by the spectral degree of coherence , h a b ( ). This quantity measures the correlation between fields that exist at two distant locations and whose respective polarizations are given in terms of angles α and β, which can be set independently from one another. Such a correlation qualifies for the construction of the Bell parameter S. By changing the amount of field correlation, we could cover a range that goes from S. Our experimental findings should provide useful material for the ongoing, theoretical discussions about the quantum-classical border.

Experimental investigation of the relation between measurement uncertainties and non-local quantum correlations

“…These experimental results all confirm the validity of the mathematical formalism without explaining the physical mechanism associated with the failure of local realism [12]. It has even been pointed out that the mathematical analogy between classical fields and probability amplitudes permits a classical violation of Bell's inequalities which is unrelated to the problem of hidden variables and realism [13,14,15,16,17,18,19]. In the light of such developments, it appears to be useful to take a closer look at the original intention of Bell's inequalities as a criterion for the possibility of measurement independent realities of the noncommuting physical properties of an individual quantum system.…”

Measurement of classical entanglement using interference fringes

“…Recently, more experiments indicate that classical entanglement has a similar property to violate the Bell-CHSH inequality which was normally regarded as a quantum behavior. In those experiments, classical light beams can attain a similar correlation level to those results in experiments of entangled quantum systems [10][11][12][13]. Therefore, the distinction between classical and quantum entanglement is not clear so that classical entanglement may provide some interesting applications previously supported by quantum entanglement.…”

Bell inequality violation and operator ordering in quantum theory

“…Such classical models have already been used to describe optical phenomena related to the vacuum fluctuations [22][23][24][25]. Moreover, the quantum-classical boundary has been recently revisited in a number of research works with the aid of new theoretical tools for characterizing polarization in different optical degrees of freedom and the corresponding correlations [26][27][28][29][30][31].…”