Thursday Colloquium
Quantum correlations in time: Macrorealism and its extreme limits
Speaker: A. R. Usha Devi (Senior Professor, Department of Physics, Bangalore University, Bangalore)
The Leggett–Garg framework probes the classical notion of macrorealism using temporal correlations obtained from sequential measurements on a single system. Traditionally, such tests rely on correlation-based inequalities, which are sensitive to measurement invasiveness.
In this colloquium, I will first review the conceptual foundations of macrorealism and the motivation behind Leggett–Garg inequalities. I will then introduce entropic Leggett–Garg inequalities, which replace correlation functions with information-theoretic quantities and provide a complementary way of detecting non-classical temporal behavior.
I will then discuss recent advances in pushing temporal quantum correlations beyond conventional bounds, including scenarios where temporal correlations approach or achieve their algebraic maximum. I will explain the physical mechanisms that enable such extremal temporal correlations.
The talk will be self-contained and aimed at a broad audience, while highlighting how temporal correlations offer both a deeper understanding of quantum foundations and new opportunities for quantum information processing.