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Quantum theory violates Bell's inequality, but not to the maximum extent that is logically possible. We derive inequalities (generalizations of Cirel'son's inequality) that quantify the upper bound of the violation, both for the standard…

Quantum Physics · Physics 2009-11-07 Dennis Dieks

Non-locality stands nowadays not only as one of the cornerstones of quantum theory, but also plays a crucial role in quantum information processing. Several experimental investigations of nonlocality have been carried out over the years. In…

The term 'locality' is used in different contexts with different meanings. There have been claims that relational quantum mechanics is local, but it is not clear then how it accounts for the effects that go under the usual name of quantum…

Quantum Physics · Physics 2019-02-20 Pierre Martin-Dussaud , Carlo Rovelli , Federico Zalamea

Contextuality is a feature of quantum correlations. It is crucial from a foundational perspective as a nonclassical phenomenon, and from an applied perspective as a resource for quantum advantage. It is commonly defined in terms of hidden…

In Bell inequality tests, the evolution of the wavefunction is not covariant, i.e. not invariant under velocity boost that change the time ordering of events, but the laws that govern the probability distribution of possible results are. In…

Quantum Physics · Physics 2010-02-09 Nicolas Gisin

This short article concentrates on the conceptual aspects of the violation of Bell inequalities, and acts as a map to the 265 cited references. The article outlines (a) relevant characteristics of quantum mechanics, such as statistical…

Quantum Physics · Physics 2021-06-29 Brian Drummond

The no-signalling principle is a fundamental assumption in Bell-inequality and quantum-steering experiments. Nonetheless, experimental imperfections can lead to apparent violations beyond those expected from finite-sample statistics. Here,…

We demonstrate extraction of randomness from spontaneous-emission events less than 36 ns in the past, giving output bits with excess predictability below $10^{-5}$ and strong metrological randomness assurances. This randomness generation…

Quantum Physics · Physics 2015-12-18 Carlos Abellan , Waldimar Amaya , Daniel Mitrani , Valerio Pruneri , Morgan W. Mitchell

The violation of Bell inequalities by experiment has convinced physicists that we cannot maintain a classical view of the world. When we argue against the possibility of local realist hidden-variable models, however, the ubiquitous…

Quantum Physics · Physics 2008-10-16 Peter Morgan

A century after the advent of Quantum Mechanics and General Relativity, both theories enjoy incredible empirical success, constituting the cornerstones of modern physics. Yet, paradoxically, they suffer from deep-rooted, so-far intractable,…

Quantum Physics · Physics 2017-03-20 Elizabeth S. Gould , Niayesh Afshordi

Quantum nonlocality may be an artifact of the assumption that observers obey the laws of classical mechanics, while observed systems obey quantum mechanics. I show that, at least in the case of Bell's Theorem, locality is restored if…

Quantum Physics · Physics 2007-05-23 Frank J. Tipler

Quantum nonlocality is typically assigned to systems of two or more well separated particles, but nonlocality can also exist in systems consisting of just a single particle, when one considers the subsystems to be distant spatial field…

Quantum Physics · Physics 2015-03-13 Libby Heaney , Adan Cabello , Marcelo F. Santos , Vlatko Vedral

It is known that "quantum non locality", leading to the violation of Bell's inequality and more generally of classical local realism, can be attributed to the conjunction of two properties, that we call here elementary locality and…

Quantum Physics · Physics 2022-01-04 Philippe Grangier

The notion of the Einstein-Podolsky-Rosen (EPR) "element of reality" is much discussed in the literature on the foundations of quantum mechanics. Recently, it has become particularly relevant due to a proposed criterion of the physical…

History and Philosophy of Physics · Physics 2020-02-20 Geoff Beck

The problem of the existence of nonlocal effects in Quantum Mechanics is discussed. The problem is divided in two: the first ('soft') one is to explain the violation of Bell's inequalities as a statistical magnitude. This can be achieved by…

Quantum Physics · Physics 2026-03-11 Alejandro A. Hnilo

Nonlocality is a distinctive feature of quantum theory, which has been extensively studied for decades. It is found that the uncertainty principle determines the nonlocality of quantum mechanics. Here we show that various degrees of…

Quantum Physics · Physics 2023-06-14 Ma-Cheng Yang , Jun-Li Li , Cong-Feng Qiao

It was recently noted the existence of an apparently discontinuous boundary between determinism and indeterminism in Quantum Mechanics. We propose to explore this boundary in an optical Bell's experiment by recording the distribution, of…

Quantum Physics · Physics 2024-08-21 Alejandro Hnilo , Marcelo Kovalsky , Mónica Agüero , Myriam Nonaka

Quantum nonlocality offers a secure way to produce random numbers: their unpredictability is intrinsic and can be certified just by observing the statistic of the measurement outcomes, without assumptions on how they are produced. To do…

The use of Bell's theorem in any application or experiment relies on the assumption of free choice or, more precisely, measurement independence, meaning that the measurements can be chosen freely. Here, we prove that even in the simplest…

Quantum Physics · Physics 2016-11-25 Gilles Pütz , Denis Rosset , Tomer Jack Barnea , Yeong-Cherng Liang , Nicolas Gisin

Quantum nonlocality is often judged by violations of Bell-type inequalities for a given state. The computation of such violations is a global task, requiring evaluation of global correlations and subsequent testing against a Bell…

Quantum Physics · Physics 2025-11-04 Rohit Kishan Ray