Leggett-Garg Macrorealism and temporal correlations

TL;DR

This paper reviews recent advances in testing macrorealism through Leggett-Garg inequalities, addressing loopholes, and exploring nonclassical temporal correlations in quantum systems.

Contribution

It provides a comprehensive overview of theoretical and experimental progress in closing loopholes and defining nonclassical temporal correlations beyond macrorealist models.

Findings

Recent experiments have closed key loopholes in Leggett-Garg tests.

New definitions of nonclassical temporal correlations have been proposed.

Applications in sequential quantum information processing have been demonstrated.

Abstract

Leggett and Garg formulated macrorealist models encoding our intuition on classical systems, i.e., physical quantities have a definite value that can be measured with minimal disturbance, and with the goal of testing macroscopic quantum coherence effects. The associated inequalities, involving the statistics of sequential measurements on the system, are violated by quantum mechanical predictions and experimental observations. Such tests, however, are subject to loopholes: a classical explanation can be recovered assuming specific models of measurement disturbance. We review recent theoretical and experimental progress in characterizing macrorealist and quantum temporal correlations, and in closing loopholes associated with Leggett-Garg tests. Finally, we review recent definitions of nonclassical temporal correlations, which go beyond macrorealist models by relaxing the assumption on the measurement disturbance, and their applications in sequential quantum information processing.