# Generalized Holevo theorem and distinguishability notions

## TL;DR

This paper generalizes the Holevo theorem using various distinguishability measures, introducing new inequalities and exploring their implications for qubit ensembles, including cases where different notions of distinguishability coincide or reveal ensemble properties.

## Contribution

It extends the Holevo theorem framework by incorporating generalized distinguishability measures, providing new inequalities and insights into qubit ensemble properties.

## Key findings

- Generalized Holevo information and accessible information are introduced.
- For two-qubit ensembles, Kolmogorov distinguishability yields equal generalized quantities.
- Bhattacharyya distinguishability captures non-commutativity and purity of ensembles.

## Abstract

We present a generalization of the Holevo theorem by means of distances used in the definition of distinguishability of states, showing that each one leads to an alternative Holevo theorem. This result involves two quantities: the generalized Holevo information and the generalized accessible information. Additionally, we apply the new inequalities to qubits ensembles showing that for the Kolmogorov notion of distinguishability (for the case of an ensemble of two qubits) the generalized quantities are equal. On the other hand, by using a known example, we show that the Bhattacharyya notion captures not only the non-commutativity of the ensemble but also its purity.