Use of quantum correlation: A theoretical and experimental perspective

Giuseppe Vitagliano, Costantino Budroni

In this Perspective, the authors review the state of the art of Leggett-Garg macrorealism and its experimental falsification and connect them with the broader framework of temporal quantum correlations. The latter, inherently related to the notion of memory of a system, is reviewed from the perspective of practical quantum information-theoretic tasks.

Jianqi Sheng, Dongkai Zhang, Lixiang Chen

Quantum theory departs from classical physics in its treatment of correlations, most prominently through the phenomena of contextuality and nonlocality. Once regarded primarily as foundational curiosities, these effects are now understood as key operational resources for quantum computation, communication, and simulation. Although traditionally investigated in distinct settings, recent theoretical and experimental advances have revealed deep conceptual, mathematical, and operational connections between them. This review presents a unified perspective on these developments based on sheaf-theoretic and graph-theoretic frameworks, which provide theory-independent characterizations of statistical correlations. These approaches clarify the structural relationship between contextuality and nonlocality, facilitate the formulation of experimentally testable inequalities, and guide implementations in realistic physical platforms, with particular emphasis on photonic systems. By bridging abstract theoretical structures and concrete experimental realizations, this review sheds light on the nonclassical foundations of quantum correlations and their emerging role in quantum technologies.

Matteo Fadel

Matteo Fadel

Shengjun Wu

Dengke Qu, Paweł Kurzyński, Dagomir Kaszlikowski +5 more

Recently, an inequality satisfied by noncontextual hidden-variable models and violated by quantum mechanics for all states of a four-level system has been derived based on an information-theoretic distance approach to nonclassical correlations. In this Rapid Communication, we experimentally demonstrate the violation of this inequality with single photons. Our experiment offers a method to study a distinction between quantum and classical correlations from an information-theoretic perspective.