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In terms of a suitable variant of the EPR–Bohm example, we argue that the quantum mechanically predicted and experimentally verified violation of a Bell-type path–spin noncontextual realist inequality for an "intraparticle" path–spin entanglement involving single neutrons can be used to infer a form of nonlocality, distinct from Bell-type nonlocality, that is required for any relevant hidden variable model to be compatible with the quantum mechanical treatment of an EPR–Bohm-type "interparticle" entanglement.

Although regarded today as an important resource in quantum information, nonlocality has yielded over the years many conceptual conundrums. Among the latter are nonlocal aspects of single particles which have been of major interest. In this paper, the nonlocality of single quanta is studied in a square nested Mach–Zehnder interferometer with spatially separated detectors using a delayed choice modification of quantum measurement outcomes that depend on the complex-valued weak values. We show that if spacelike separated Bob and Alice are allowed to freely control their quantum devices, the geometry of the setup constrains the local hidden variable models. In particular, hidden signaling and a list of contextual instructions are required to split a quantum state characterized by a positive Wigner function into two quantum states with nonpositive Wigner functions. This implies that local hidden variable models could rely neither on only two hidden variables for position and momentum, nor on simultaneous factorizability of both the hidden probability densities and weights of splitting to reproduce the correct quantum distributions. While our analysis does not fully exclude the existence of nonfactorizable local hidden variable models, it demonstrates that the recently proposed weak values of quantum histories necessitate contextual splitting of prior commitments to measurement outcomes, due to functional dependence on the total Feynman sum that yields the complex-valued quantum probability amplitude for the studied quantum transition. This analysis also highlights the quantum nature of weak measurements.

An empirical model is a generalization of a probability space. It consists of a simplicial complex of subsets of a class 𝒳 of random variables such that each simplex has an associated probability distribution. The ensuing marginalizations are coherent, in the sense that the distribution on a face of a simplex coincides with the marginal of the distribution over the entire simplex. An empirical model is called contextual if its distributions cannot be obtained by marginalizing a joint distribution over 𝒳. Contextual empirical models arise naturally in quantum theory, giving rise to some of its counter -intuitive statistical consequences. In this paper, we present a different and classical source of contextual empirical models: the interaction among many stochastic processes. We attach an empirical model to the ensuing network in which each node represents an open stochastic process with input and output random variables. The statistical behaviour of the network in the long run makes the empirical model generically contextual and even strongly contextual.

It is suggested that the “B” in QBism rightfully stands for Bohr. The paper begins by explaining why Bohr seems obscure to most physicists. Having identified the contextuality of physical quantities as Bohr’s essential contribution to Kant’s theory of science, it outlines the latter, its own contextuality (human experience), and its decontextualization. In order to preserve the decontextualization achieved by Kant’s theory, Bohr seized on quantum phenomena as the principal referents of atomic physics, all the while keeping the universal context of human experience at the center of his philosophy. QBism, through its emphasis on the individual experiencing subject, brings home the intersubjective constitution of objectivity more forcefully than Bohr ever did. If measurements are irreversible and outcomes definite, it is because the experiences of each subject are irreversible and definite. Bohr’s insights, on the other hand, are exceedingly useful in clarifying the QBist position, attenuating its excesses, and enhancing its internal consistency.

It is well known that correlations produced by common causes in the past cannot violate Bell’s inequalities. This was emphasized by Bell in his celebrated example of Bertlmann’s socks. However, if common causes are induced by the very measurement process i.e., actualized at each run of a joint measurement, in a way that depends on the type of joint measurement that is being executed (hence, the common causes are contextually actualized), the resulting correlations are able to violate Bell’s inequalities, thus providing a simple and general explanation for the origin of quantum correlations. We illustrate this mechanism by revisiting Bertlmann’s socks example. In doing so, we also emphasize that Bell’s inequalities, in their essence, are about demarcating ‘non-induced by measurements’ (non-contextual) from ‘induced by measurements’ (contextual) common causes, where the latter would operate at a non-spatial level of our physical reality, when the jointly measured entangled entities are microscopic in nature.

The view exists that Bell-tests would only be about local incompatibility of quantum observables and that quantum non-locality would be an unnecessary concept in physics. In this note, we emphasize that it is not incompatibility at the local level that is important for the violation of Bell-CHSH inequality, but incompatibility at the non-local level of the joint measurements. Hence, non-locality remains a necessary concept to properly interpret the outcomes of certain joint quantum measurements.

We apply Shannon’s entropy of information to a quantum computational model of the universe to discuss how big the future could be relative to a given present. We discuss how such a model could provide a basis for an endophysical description of the universe.

The aim of this article is to give an introductory survey to the quantum cognitive approach to concepts. We first review the fundamental problems in the modeling of concepts. Next we show how the quantum cognition program for modeling concepts and their combinations is able to cope with these problems. Finally, we elaborate on some of the most recent developments that deepen the structural relations between quantum entities and concepts. As a conducting line, we have followed the contributions of the Brussels group of quantum cognition directed by Diederik Aerts.

In this work we develop a modal structure for the simultaneous treatment of actual and possible properties of quantum systems. A logical system based on orthomodular lattices enriched with a modal operator is given, obtaining algebraic completeness and completeness with respect to a Kripke-style semantic. We show that, in spite of the fact that, the language is enriched with the addition of a modal operator, contextuality remains a central feature of quantum systems.