Quantumness of pure-state ensembles via coherence of Gram matrix based on generalized $\alpha$-$z$-relative R\'enyi entropy

TL;DR

This paper introduces a new measure for the quantumness of pure-state ensembles using the generalized $oldsymbol{ extalpha}$-$oldsymbol{ extz}$-relative R{é}nyi entropy of coherence applied to the Gram matrix, providing insights into their properties and comparisons.

Contribution

It proposes a novel quantumness measure based on generalized R{é}nyi entropy, extending previous coherence-based approaches and analyzing its properties and applications.

Findings

The new measure effectively quantifies the quantumness of various pure-state ensembles.

Comparison with existing measures highlights unique features and ordering.

Application to six important ensembles demonstrates its practical usefulness.

Abstract

The Gram matrix of a set of quantum pure states plays key roles in quantum information theory. It has been highlighted that the Gram matrix of a pure-state ensemble can be viewed as a quantum state, and the quantumness of a pure-state ensemble can thus be quantified by the coherence of the Gram matrix [Europhys. Lett. \textbf{134} 30003]. Instead of the $l_1$-norm of coherence and the relative entropy of coherence, we utilize the generalized $\alpha$-$z$-relative R\'enyi entropy of coherence of the Gram matrix to quantify the quantumness of a pure-state ensemble and explore its properties. We show the usefulness of this quantifier by calculating the quantumness of six important pure-state ensembles. Furthermore, we compare our quantumness with other existing ones and show their features as well as orderings.