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We show that the "practical" Bell inequalities, which use intensities as the observed variables, commonly used in quantum optics and widely accepted in the community, suffer from an inherent loophole, which severely limits the range of…

Quantum Physics · Physics 2016-10-07 Marek Zukowski , Marcin Wiesniak , Wieslaw Laskowski

Quantum correlations which violate a Bell inequality are presumed to power better-than-classical protocols for solving communication complexity problems (CCPs). How general is this statement? We show that violations of correlation-type Bell…

Quantum Physics · Physics 2020-09-09 Armin Tavakoli , Marek Żukowski , Časlav Brukner

Bell inequalities are mathematical constructs that demarcate the boundary between quantum and classical physics. A new class of multiplicative Bell inequalities originating from a volume maximization game (based on products of correlators…

Investigations of the boundary of the quantum correlation set through the derivation of quantum Bell inequalities have gained increased attention in recent years, which are related to Tsirelson's problem and have significant applications in…

Quantum Physics · Physics 2024-10-02 Yuan Liu , Ho Yiu Chung , Ravishankar Ramanathan

Correlations for the Bell gedankenexperiment are constructed using probabilities given by quantum mechanics, and nonlocal information. They satisfy Bell's inequality and exhibit spatial non stationarity in angle. Correlations for three…

Quantum Physics · Physics 2015-06-26 Louis Sica

Incompatible, i.e. non-jointly measurable quantum measurements are a necessary resource for many information processing tasks. It is known that increasing the number of distinct measurements usually enhances the incompatibility of a…

Quantum Physics · Physics 2023-09-28 Lucas Tendick , Hermann Kampermann , Dagmar Bruß

Bell inequalities or Bell-like experiments are supposed to test hidden variable theories based on three intuitive assumptions: determinism, locality and measurement independence. If one of the assumptions of Bell inequality is properly…

Quantum Physics · Physics 2018-04-19 R. Rossi , Leonardo A. M. Souza

Bell inequalities have traditionally been used to demonstrate that quantum theory is nonlocal, in the sense that there exist correlations generated from composite quantum states that cannot be explained by means of local hidden variables.…

Some new Bell inequalities for consecutive measurements are deduced under joint realism assumption, using some perfect correlation property. No locality condition is needed. When the measured system is a macroscopic system, joint realism…

Quantum Physics · Physics 2009-11-13 Ramon Lapiedra

The logical foundations of Bell's inequality are reexamined. We argue that the form of the reality condition that underpins Bell's inequality comes from the requirement of solving the quantum measurement problem. Hence any violation of…

Quantum Physics · Physics 2008-02-19 John V. Corbett , Dipankar Home

Correlations that cannot be reproduced with local variables certify the generation of private randomness. Usually, the violation of a Bell inequality is used to quantify the amount of randomness produced. Here, we show how private…

Quantum Physics · Physics 2014-04-16 Jean-Daniel Bancal , Lana Sheridan , Valerio Scarani

The observation of quantum nonlocality, i.e. quantum correlations violating a Bell inequality, implies the use of incompatible local quantum measurements. Here we consider the converse question. That is, can any set of incompatible…

Quantum Physics · Physics 2016-06-06 Marco Túlio Quintino , Joseph Bowles , Flavien Hirsch , Nicolas Brunner

Bell's theorem supposedly demonstrates an irreconcilable conflict between quantum mechanics and local, realistic hidden variable theories. Most proofs of Bell's theorem, are based on inequalities. In this paper we present an alternative…

Quantum Physics · Physics 2025-03-10 Andrea Aiello

Quantum correlations between spatially separated parts of a $d$-dimensional bipartite system ($d\geq 2$) have no classical analog. Such correlations, also called entanglements, are not only conceptually important, but also have a profound…

Bell nonlocality is the resource that enables device-independent quantum information processing tasks. It is revealed through the violation of so-called Bell inequalities, indicating that the observed correlations cannot be reproduced by…

Quantum Physics · Physics 2024-09-25 Patrick Emonts , Mengyao Hu , Albert Aloy , Jordi Tura

The violation of a Bell inequality is an experimental observation that forces one to abandon a local realistic worldview, namely, one in which physical properties are (probabilistically) defined prior to and independent of measurement and…

Bell inequalities rest on three fundamental assumptions: realism, locality, and free choice, which lead to nontrivial constraints on correlations in very simple experiments. If we retain realism, then violation of the inequalities implies…

Quantum Physics · Physics 2021-05-20 Pawel Blasiak , Emmanuel M. Pothos , James M. Yearsley , Christoph Gallus , Ewa Borsuk

This paper analyzes effects of time-dependence in the Bell inequality. A generalized inequality is derived for the case when coincidence and non-coincidence [and hence whether or not a pair contributes to the actual data] is controlled by…

Quantum Physics · Physics 2022-03-16 Jan-Åke Larsson , Richard Gill

Bell inequalities play a central role in the study of quantum non-locality and entanglement, with many applications in quantum information. Despite the huge literature on Bell inequalities, it is not easy to find a clear conceptual answer…

Quantum Physics · Physics 2012-06-21 Samson Abramsky , Lucien Hardy

Quantum theory predicts and experiments confirm that nature can produce correlations between distant events that are nonlocal in the sense of violating a Bell inequality. Nevertheless, Bell's strong sentence {\it Correlations cry out for…