Information causality A broad class of theories exist which share the distinguishing characteristics of quantum mechanics, but allow even stronger correlations. Therefore a criterion that could be used to distinguish physical theories from non-physical ones would be of considerable value. The principle of 'information causality', introduced here by Marcin Pawłowski et al., may provide just this. The principle states that communication of m classical bits causes information gain of at most m bits. The authors show that it is respected by classical and quantum physics, but violated by other models that resemble quantum mechanics but with stronger correlations. The principle is a generalization of the no-signalling condition (information cannot be transmitted faster than light) and may be a foundational property of nature.
Information causality A broad class of theories exist which share the distinguishing characteristics of quantum mechanics, but allow even stronger correlations. Therefore a criterion that could be used to distinguish physical theories from non-physical ones would be of considerable value. The principle of 'information causality', introduced here by Marcin Pawłowski et al., may provide just this. The principle states that communication of m classical bits causes information gain of at most m bits. The authors show that it is respected by classical and quantum physics, but violated by other models that resemble quantum mechanics but with stronger correlations. The principle is a generalization of the no-signalling condition (information cannot be transmitted faster than light) and may be a foundational property of nature.
Quantum mechanics is not the unique no-signaling theory which is endowed with stronger-than-classical correlations, and there exists a broad class of no-signaling theories allowing even stronger-than-quantum correlations. The principle of information causality has been suggested to distinguish quantum theory from these nonphysical theories, together with an elegant information-theoretic proof of the quantum bound of two-particle correlations. In this work, we extend this to genuine N-particle correlations that cannot be reduced to mixtures of states in which a smaller number of particles are entangled. We first express Svetlichny's inequality in terms of multipartite no-signaling boxes, then prove that the strongest genuine multipartite correlations lead to the maximal violation of information causality. The maximal genuine multipartite correlations under the constraint of information causality is found to be equal to the quantum mechanical bound. This result consolidates information causality as a physical principle defining the possible correlations allowed by nature, and provides intriguing insights into the limits of genuine multipartite correlations in quantum theory.
Quantum mechanics is not the unique no-signaling theory which is endowed with stronger-than-classical correlations, and there exists a broad class of no-signaling theories allowing even stronger-than-quantum correlations. The principle of information causality has been suggested to distinguish quantum theory from these nonphysical theories, together with an elegant information-theoretic proof of the quantum bound of two-particle correlations. In this work, we extend this to genuine N-particle correlations that cannot be reduced to mixtures of states in which a smaller number of particles are entangled. We first express Svetlichny's inequality in terms of multipartite no-signaling boxes, then prove that the strongest genuine multipartite correlations lead to the maximal violation of information causality. The maximal genuine multipartite correlations under the constraint of information causality is found to be equal to the quantum mechanical bound. This result consolidates information causality as a physical principle defining the possible correlations allowed by nature, and provides intriguing insights into the limits of genuine multipartite correlations in quantum theory.
Quantum correlations can be stronger than anything achieved by classical systems, yet they are not reaching the limit imposed by relativity. The principle of information causality offers a possible explanation for why the world is quantum and why there appear to be no even stronger correlations. Generalizing the no-signaling condition it suggests that the amount of accessible information must not be larger than the amount of transmitted information. Here we study this principle experimentally in the classical, quantum and post-quantum regimes. We simulate correlations that are stronger than allowed by quantum mechanics by exploiting the effect of polarization-dependent loss in a photonic Bell-test experiment. Our method also applies to other fundamental principles and our results highlight the special importance of anisotropic regions of the no-signalling polytope in the study of fundamental principles.
Quantum systems are able to show correlations between its parties that are stronger than correlations found in classical systems. Some of those strong correlations are called nonlocal, as for the classical correlations, they are calledlocal. Nonlocal correlations do not imply long-distance actions or superluminal communication, because they satisfy the nonsignaling condition. There are nonsignaling correlations stronger than quantum correlations because the quantum correlation set is a strictsubset of the nonsignaling correlation set. Quantum correlations are determined by how one obtains the probabilities of geting results conditioned to the measurement choices, considering the density operator describing the quantum state and the set of measurements. Moreover, a physical principle capable of justify quantum nonlocality is unkown. Because of that, an important question appeared:Would there be a physical principle which is able to explain the quantum nonlocality limits? Within the attempt to reach a positive answer for this question, some principles were presented in the last years. One of the most highlighted ones is the so-calledInformation Causality. This principle states that when one considers a system with two correlationedparties and the sending of a message from one party to the other containingd bits of information, the information gain within this process is limited tod bits. Quantum correlations satisfy the Information Causality principle. The best criteria known for the principle are able to discard most of the nonsignaling correlations that are stronger than quantum correlations, in the most simple scenarios. However, there still are supra-quantum correlations that obey such criteria. Recently, a new approach has been adopted for the achievement of a stronger criteriontorepresenttheInformationCausalityprinciple.Suchapproachisbasedonclassicaland quantum information theory, and causal inference theory, the latter being a powerful and interesting theory that relates the correlations with causal relations. This theory has found applications in many areas.This thesis presents the main elements of information theory, causal inference theory and nonlocality, aiming the analysis of the Information Causality principle and its strongest criterion. The main results obtained for the principle will be revised, and it will be presented a partial result obtained for a generalization of the more recent Information Causality criterion by considering scenarios in which multiple copies of the nonlocal resource are available.
Information causality (IC) was introduced as a physical principle constraining correlations in non-signaling theories. Whether it can recover the exact quantum correlation boundary, beyond Uffink's inequality, has remained an open question. Here, we combine its generalized formulation for correlated inputs with a new communication protocol to derive quantum Bell inequalities that exactly characterize the quantum correlations in the simplest bipartite Bell scenario, with two binary measurements. In particular, we derive the Tsirelson-Landau-Masanes criterion directly from IC. Thus, the generalized IC implies macroscopic locality, while we also present macroscopically local correlations that violate the generalized IC. This establishes that generalized IC is a strictly stronger principle in this scenario. Together with our earlier result that generalized IC implies a nontrivial communication complexity principle, these findings strengthen the role of information causality in explaining the limits of quantum nonlocality and provide a systematic route to deriving tighter bounds on the set of quantum correlations in more general Bell scenarios.
Information causality (IC) posits that communicating m classical bits cannot give the receiver access to more than m bits of information about the sender's independent data. Although IC holds in quantum theory and excludes a broad class of supra-quantum correlations, its validity for the almost-quantum set has remained open. This semidefinite relaxation of the quantum set satisfies nontrivial communication complexity, no advantage for non-local computation, macroscopic locality, local orthogonality, and numerical evidence has suggested that it may also satisfy IC. Here we show that almost-quantum correlations violate IC, and do so without bound. Unlike earlier violations of IC, which rely on biased guesses, ours is driven by zero-error certificates: each is rare but never wrong, carries information linear in its probability, and vouches for many of the sender's bits at once. This establishes a sharp dichotomy: either IC is a valid physical principle that excludes these correlations, or any nonsignalling theory realizing them admits no mutual information obeying consistency, data processing and the chain rule. In the latter case, we discuss why the chain rule is the natural property to relinquish, and how this possibility relates to histories-based formulations and to locality defined relative to the state rather than presupposed in a fixed spacetime.