Entropic and trace distance based measures of non-Markovianity

TL;DR

This paper compares various measures of non-Markovianity in open quantum systems, revealing that trace norm-based measures can detect non-Markovianity where entropic measures cannot, indicating their greater sensitivity.

Contribution

It introduces a comparison between trace norm and entropic measures of non-Markovianity, showing that trace norm-based measures are strictly more sensitive in certain quantum dynamics.

Findings

Trace norm-based measure detects non-Markovianity where entropic measures do not.

Explicit qubit dynamics example demonstrating the difference.

Trace norm measure is strictly stronger than entropic measures.

Abstract

We analyze and compare different measures for the degree of non-Markovianity in the dynamics of open quantum systems. These measures are based on the distinguishability of quantum states which is quantified, on the one hand, by the trace distance or, more generally, by the trace norm of the Helstrom matrix, and, on the other hand, by entropic quantifiers: the Jensen-Shannon divergence, the Holevo or the quantum skew divergence. We explicitly construct a qubit dynamics for which the trace norm based non-Markovianity measure is nonzero, while all the entropic measures turn out to be zero. This leads to the surprising conclusion that the non-Markovianity measure which employs the trace norm of the Helstrom matrix is strictly stronger than all entropic non-Markovianity measures.