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Entanglement and its consequences - in particular the violation of Bell inequalities, which defies our concepts of realism and locality - have been proven to play key roles in Nature by many experiments for various quantum systems.…

We consider quantum systems composed of $N$ qubits, and the family of all Bell's correlation inequalities for two two-valued measurements per site. We show that if a $N$-qubit state $\rho$ violates any of these inequalities, then it is at…

Quantum Physics · Physics 2009-11-07 A. Acin , V. Scarani , M. M. Wolf

We consider Bell tests in which the distant observers can perform local filtering before testing a Bell inequality. Notably, in this setup, certain entangled states admitting a local hidden variable model in the standard Bell scenario can…

Quantum Physics · Physics 2016-12-01 Flavien Hirsch , Marco Túlio Quintino , Joseph Bowles , Tamás Vértesi , Nicolas Brunner

We present a prescription for obtaining Bell's inequalities for N>2 observers involving more than two alternative measurement settings. We give examples of some families of such inequalities. The inequalities are violated by certain classes…

Quantum Physics · Physics 2007-05-23 C. Brukner , W. Laskowski , T. Paterek , M. Zukowski

A set of Bell inequalities classifying the quantum entanglement of four-qubit states is presented. These inequalities involve only two measurement settings per observer and can characterize fully separable, bi-separable and tri-separable…

Quantum Physics · Physics 2013-07-26 Hui Zhao , Xing-Hua Zhang , Shao-Ming Fei , Zhi-Xi Wang

With Bell's inequalities one has a formal expression to show how essentially all local theories of natural phenomena that are formulated within the framework of realism may be tested using a simple experimental arrangement. For the case of…

General Physics · Physics 2017-03-30 Thomas Schürmann

We present a phase space formalism to evaluate Bell inequality violations in continuous variable systems. By doing so we can generalize previous analyses (which have dealt only with pure states) to arbitrary mixed states. We leverage these…

Quantum Physics · Physics 2025-01-09 Gurpahul Singh , Kelly Wurtz , Eduardo Martín-Martínez

The violation of Bell inequalities where both detection and locality loopholes are closed is crucial for device independent assessments of quantum information. While of technological nature, the simultaneous closing of both loopholes still…

Quantum Physics · Physics 2015-06-17 Colin Teo , Jiří Minář , Daniel Cavalcanti , Valerio Scarani

Quantum correlations in observables of multiple systems not only are of fundamental interest, but also play a key role in quantum information processing. As a signature of these correlations, the violation of Bell inequalities has not been…

Entanglement, describing the inseparability of a quantum multiparty system, is one of the most intriguing features of quantum mechanics. Violation of Bell inequality, for ruling out the possibility of local hidden variable theories, is…

Quantum Physics · Physics 2017-04-21 Xianxin Guo , Yefeng Mei , Shengwang Du

Bipartite Bell inequalities can be simultaneously violated by two different pairs of observers when weak measurements and signaling is employed. Here we experimentally demonstrate the violation of two simultaneous CHSH inequalities by…

Quantum Physics · Physics 2017-04-10 Matteo Schiavon , Luca Calderaro , Mirko Pittaluga , Giuseppe Vallone , Paolo Villoresi

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…

We present a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states $\left|G_{abcd}\right >$ [Phys. Rev. A 65, 052112 (2002)] and several canonical four-qubit…

Quantum Physics · Physics 2017-06-07 Dong Ding , Fengli Yan , Ting Gao

Various Bell inequalities are trivial algebraic properties satisfied by each line of particular data spreadsheets.It is surprising that their violation in some experiments, allows to speculate about the existence of nonlocal influences in…

Quantum Physics · Physics 2020-09-25 Marian Kupczynski

In this paper we obtain violations of general bipartite Bell inequalities of order $\frac{\sqrt{n}}{\log n}$ with $n$ inputs, $n$ outputs and $n$-dimensional Hilbert spaces. Moreover, we construct explicitly, up to a random choice of signs,…

Quantum Physics · Physics 2011-08-30 Marius Junge , Carlos Palazuelos

We present a generalized Bell inequality for two entangled quNits. On one quNit the choice is between two standard von Neumann measurements, whereas for the other quNit there are $N^2$ different binary measurements. These binary…

Quantum Physics · Physics 2007-05-23 H. Bechmann-Pasquinucci , N. Gisin

Bell's test, initially devised to distinguish quantum theory from local hidden variable models through {violations of local bounds}, is also a common tool for detecting entanglement. For this purpose, one can assume the quantum description…

Quantum Physics · Physics 2026-04-21 Liang-Liang Sun , Yong-Shun Song , Sixia Yu

Bell inequalities constitute a key tool in quantum information theory: they not only allow one to reveal nonlocality in composite quantum systems, but, more importantly, they can be used to certify relevant properties thereof. We provide a…

Quantum Physics · Physics 2020-01-22 F. Baccari , R. Augusiak , I. Šupić , J. Tura , A. Acín

Violations of Bell inequalities in classical optics have been demonstrated in terms of field mean intensities and correlations, however, the quantum meaning of violations point to statistics and probabilities. We present a violation of Bell…

Quantum Physics · Physics 2023-01-31 Laura Ares , Alfredo Luis

D\"{u}r [Phys. Rev. Lett. {\bf 87}, 230402 (2001)] constructed $N$-qubit bound entangled states which violate a Bell inequality for $N\ge 8$, and his result was recently improved by showing that there exists an $N$-qubit bound entangled…

Quantum Physics · Physics 2013-05-29 Dong Pyo Chi , Kabgyun Jeong , Taewan Kim , Kyungjin Lee , Soojoon Lee