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Density matrices are the most general descriptions of quantum states, covering both pure and mixed states. Positive semidefiniteness is a physical requirement of density matrices, imposing nonnegative probabilities of measuring physical…

Quantum Physics · Physics 2024-09-11 Colm Kelleher

Two distant systems can exhibit quantum nonlocality even though the correlations between them admit a local model. This nonlocality can be revealed by testing extra correlations between successive measurements on one of the systems which do…

Quantum Physics · Physics 2014-11-20 Adan Cabello

With the goal of gaining a deeper understanding of quantum non-locality, we decompose quantum correlations into more elementary non-local correlations. We show that the correlations of all pure entangled states of two qubits can be…

Quantum Physics · Physics 2009-11-13 Nicolas Brunner , Nicolas Gisin , Sandu Popescu , Valerio Scarani

Quantum nonlocality is a kind of significant quantum correlation that is stronger than quantum entanglement and EPR steering. The standard tripartite nonlocality can be detected by the violation of the Mermin inequality. By using local…

Quantum Physics · Physics 2022-05-24 Qiao-Qiao Lv , Jin-Min Liang , Zhi-Xi Wang , Shao-Ming Fei

Quantum nonlocality without entanglement (Q-NWE) encapsulates nonlocal behavior of multipartite product states as they may entail global operation for optimal decoding of the classical information encoded within. Here we show that the…

Quantum Physics · Physics 2020-03-25 Some Sankar Bhattacharya , Sutapa Saha , Tamal Guha , Manik Banik

Superunsteerability is a particular kind of spatial quantum correlation that can be observed in a steering scenario in the presence of limited shared randomness. In this work, we define an experimentally measurable quantity in a steering…

Quantum Physics · Physics 2023-07-19 Chellasamy Jebarathinam , Debarshi Das

Consider a bipartite quantum system with at least one of its two components being itself a composite system. By tracing over part of one (or both) of these two subsystems it is possible to obtain a reduced (separable) state that exhibits…

Quantum Physics · Physics 2015-04-10 Guido Bellomo , Ana P. Majtey , A. R. Plastino , A. Plastino

Steerability is a characteristic of quantum correlations lying in between entanglement and Bell nonlocality. Understanding how these steering correlations can be shared between different parties has profound applications in ensuring…

Quantum Physics · Physics 2020-11-11 Biswajit Paul , Kaushiki Mukherjee

Quantum systems that have never interacted can become nonlocally correlated through a process called entanglement swapping. To characterize nonlocality in this context, we introduce local models where quantum systems that are initially…

Quantum Physics · Physics 2010-04-27 Cyril Branciard , Nicolas Gisin , Stefano Pironio

Due to the importance of entanglement for quantum information purposes, a framework has been developed for its characterization and quantification as a resource based on the following operational principle: entanglement among $N$ parties…

Quantum Physics · Physics 2013-05-30 Rodrigo Gallego , Lars E. Würflinger , Antonio Acín , Miguel Navascués

The violations of Bell inequalities by measurements on quantum states give rise to the phenomenon of quantum non-locality and express the advantage of using quantum resources over classical ones for certain information-theoretic tasks. The…

Quantum Physics · Physics 2020-11-30 Abderramán Amr , Carlos Palazuelos , Julio I. de Vicente

The outcomes of measurements on entangled quantum systems can be nonlocally correlated. However, while it is easy to write down toy theories allowing arbitrary nonlocal correlations, those allowed in quantum mechanics are limited. Quantum…

Quantum Physics · Physics 2015-03-17 Peter Janotta , Christian Gogolin , Jonathan Barrett , Nicolas Brunner

Quantum steering refers to correlations that can be classified as intermediate between entanglement and Bell nonlocality. Every state exhibiting Bell nonlocality exhibits also quantum steering and every state exhibiting quantum steering is…

Quantum Physics · Physics 2021-06-08 Dawid Maskalaniec , Karol Bartkiewicz

Quantum theory features several phenomena which can be considered as resources for information processing tasks. Some of these effects, such as entanglement, arise in a nonlocal scenario, where a quantum state is distributed between…

Quantum Physics · Physics 2024-07-22 Martin Plávala , Otfried Gühne

Nonlocal correlations arising from measurements on tripartite entangled states can be classified into two groups, one genuinely $3-$way nonlocal and other local with respect to some bipartition. Still, whether a genuinely tripartite…

Quantum Physics · Physics 2016-11-15 Biswajit Paul , Kaushiki Mukherjee , Debasis Sarkar

It has been suggested that there may exist quantum correlations that go beyond entanglement. The existence of such correlations can be revealed by quantum discord, but not by the conventional measure of entanglement. We argue that a state…

Quantum Physics · Physics 2016-09-30 Pankaj Agrawal , Sk Sazim , Indranil Chakrabarty , Arun K. Pati

Quantum steering is observed when performing appropriate local measurements on an entangled state. Here we discuss the possibility of simulating classically this effect, using classical communication instead of entanglement. We show that…

Quantum Physics · Physics 2016-07-14 Ana Belén Sainz , Leandro Aolita , Nicolas Brunner , Rodrigo Gallego , Paul Skrzypczyk

We give a set of necessary conditions for locality in bipartite systems, which include and generalize known Bell's inequalities. Each condition corresponds to a specific order of the expansion of random variables defined on graphs, in terms…

We study the relations between quantum coherence and quantum nonlocality, genuine quantum entanglement and genuine quantum nonlocality. We show that the coherence of a qubit state can be converted to the nonlocality of two-qubit states via…

Quantum Physics · Physics 2019-09-04 Ya Xi , Tinggui Zhang , Zhujun Zheng , Xianqing Li-Jost , Shao-Ming Fei

The behaviour under particle loss of entanglement and nonlocality is investigated in multipartite quantum systems. In particular, we define a notion of persistency of nonlocality, which leads to device-independent tests of persistent…

Quantum Physics · Physics 2012-10-16 Nicolas Brunner , Tamas Vertesi