Search results for: BELL INEQUALITY

Quantum communication complexity advantage implies violation of a Bell inequality
PublicationWe obtain a general connection between a quantum advantage in communication complexity and nonlocality. We show that given any protocol offering a (sufficiently large) quantum advantage in communication complexity, there exists a way of obtaining measurement statistics which violate some Bell inequality. Our main tool is portbased teleportation. If the gap between quantum and classical communication complexity can grow arbitrarily...

Tradeoffs in multiparty Bellinequality violations in qubit networks
PublicationTwo overlapping bipartite binary input Bell inequalities cannot be simultaneously violated as this would contradict the usual nosignalling principle. This property is known as monogamy of Bell inequality violations and generally Bell monogamy relations refer to tradeoffs between simultaneous violations of multiple inequalities. It turns out that multipartite Bell inequalities admit weaker forms of monogamies that allow for violations...

Bound on Bell inequalities by fraction of determinism and reverse triangle inequality
PublicationIt is an established fact that entanglement is a resource. Sharing an entangled state leads to nonlocal correlations and to violations of Bell inequalities. Such nonlocal correlations illustrate the advantage of quantum resources over classical resources. In this paper, we quantitatively study Bell inequalities with 2 × n inputs. As found in Gisin et al. [Int. J. Quantum. Inform. 05, 525 (2007)], quantum mechanical correlations...

Intrinsic asymmetry with respect to adversary: a new feature of Bell inequalities
PublicationIt is known that the local bound of a Bell inequality is sensitive to the knowledge of the external observer about the settings statistics. Here we ask how that sensitivity depends on the structure of that knowledge. It turns out that in some cases it may happen that the local bound is much more sensitive to the adversaryʼs knowledge about the settings of one party than the other. Remarkably, there are Bell inequalities which are...

Strong Monogamies of NoSignaling Violations for Bipartite Correlation Bell Inequalities
PublicationThe phenomenon of monogamy of Bell inequality violations is interesting both from the fundamental perspective as well as in cryptographic applications such as the extraction of randomness and secret bits. In this article, we derive new and stronger monogamy relations for violations of Bell inequalities in general nosignaling theories. These relations are applicable to the class of binary output correlation inequalities known as...

Robust amplification of SanthaVazirani sources with three devices
PublicationWe demonstrate that amplification of arbitrarily weak randomness is possible using quantum resources. We present a randomness amplification protocol that involves Bell experiments. We find a Bell inequality which can amplify arbitrarily weak randomness and give a detailed analysis of the protocol involving it. Our analysis includes finding a sufficient violation of Bell inequality as a function of the initial quality of randomness....

Quantum Steering Inequality with Tolerance for MeasurementSetting Errors: Experimentally Feasible Signature of Unbounded Violation
Publicationuantum steering is a relatively simple test for proving that the values of quantummechanical measurement outcomes come into being only in the act of measurement. By exploiting quantum correlations, Alice can influence — steer — Bob ’ s physical system in a way that is impossible in classical mechanics, as shown by the violation of steering inequalities. Demonstrating this and similar quantum effects for systems of increasing size,...

Free randomness amplification using bipartite chain correlations
PublicationA direct analysis of the task of randomness amplification from SanthaVazirani sources using the violation of the chained Bell inequality is performed in terms of the convex combination of nosignaling boxes required to simulate quantum violation of the inequality. This analysis is used to find the exact threshold value of the initial randomness parameter from which perfect randomness can be extracted in the asymptotic limit of...

Randomness Amplification under Minimal Fundamental Assumptions on the Devices
PublicationRecently, the physically realistic protocol amplifying the randomness of SanthaVazirani sources producing cryptographically secure random bits was proposed; however, for reasons of practical relevance, the crucial question remained open regarding whether this can be accomplished under the minimal conditions necessary for the task. Namely, is it possible to achieve randomness amplification using only two nosignaling components...

Elemental and tight monogamy relations in nonsignaling theories
PublicationPhysical principles constrain the way nonlocal correlations can be distributed among distant parties. These constraints are usually expressed by monogamy relations that bound the amount of Bell inequality violation observed among a set of parties by the violation observed by a different set of parties. We prove here that much stronger monogamy relations are possible for nonsignaling correlations by showing how nonlocal correlations...

Entanglement and Nonlocality are Inequivalent for Any Number of Parties
PublicationUnderstanding the relation between nonlocality and entanglement is one of the fundamental problems in quantum physics. In the bipartite case, it is known that these two phenomena are inequivalent, as there exist entangled states of two parties that do not violate any Bell inequality. However, except for a single example of an entangled threequbit state that has a local model, almost nothing is known about such a relation in multipartite...

Realistic noisetolerant randomness amplification using finite number of devices
PublicationRandomness is a fundamental concept, with implications from security of modern data systems, to fundamental laws of nature and even the philosophy of science. Randomness is called certified if it describes events that cannot be predetermined by an external adversary. It is known that weak certified randomness can be amplified to nearly ideal randomness using quantummechanical systems. However, so far, it was unclear whether randomness amplification...

Complementarity between entanglementassisted and quantum distributed random access code
PublicationCollaborative communication tasks such as random access codes (RACs) employing quantum resources have manifested great potential in enhancing information processing capabilities beyond the classical limitations. The two quantum variants of RACs, namely, quantum random access code (QRAC) and the entanglementassisted random access code (EARAC), have demonstrated equal prowess for a number of tasks. However, there do exist specific...

A Loophole of All ‘LoopholeFree’ BellType Theorems
PublicationBell’s theorem cannot be proved if complementary measurements have to be represented by random variables which cannot be added or multiplied. One such case occurs if their domains are not identical. The case more directly related to the Einstein–Rosen–Podolsky argument occurs if there exists an ‘element of reality’ but nevertheless addition of complementary results is impossible because they are represented by elements from different...

Deviceindependent quantum key distribution based on measurement inputs
PublicationWe provide an analysis of a family of deviceindependent quantum key distribution (QKD) protocols that has the following features. (a) The bits used for the secret key do not come from the results of the measurements on an entangled state but from the choices of settings. (b) Instead of a single security parameter (a violation of some Bell inequality) a set of them is used to estimate the level of trust in the secrecy of the key....

Relationship between semi and fullydeviceindependent protocols
PublicationWe study the relation between semi and fully device independent protocols. As a tool, we use the correspondence between Bell inequalities and dimension witnesses. We present a method for converting the former into the latter and vice versa. This relation provides us with interesting results for both scenarios. First, we find new random number generation protocols with higher bit rates for both the semi and fully device independent...