The sudden change phenomenon of quantum discord

TL;DR

This paper reviews the sudden change phenomenon of quantum discord, highlighting its discovery, interpretations, experimental verifications, and its significance in quantum measurement and dynamics, while discussing open questions for future research.

Contribution

It provides a comprehensive review of the sudden change phenomenon of quantum discord, including its theoretical foundations, experimental evidence, and implications in quantum measurement and dynamics.

Findings

Uncovering of the sudden change phenomenon in quantum discord.

Experimental verification of the phenomenon.

Identification of open questions and future research directions.

Abstract

Even if the parameters determining a system's state are varied smoothly, the behavior of quantum correlations alike to quantum discord, and of its classical counterparts, can be very peculiar, with the appearance of non-analyticities in its rate of change. Here we review this sudden change phenomenon (SCP) discussing some important points related to it: Its uncovering, interpretations, and experimental verifications, its use in the context of the emergence of the pointer basis in a quantum measurement process, its appearance and universality under Markovian and non-Markovian dynamics, its theoretical and experimental investigation in some other physical scenarios, and the related phenomenon of double sudden change of trace distance discord. Several open questions are identified, and we envisage that in answering them we will gain significant further insight about the relation between the SCP and the symmetry-geometric aspects of the quantum state space.